This is just a looooong list of things i have figured out, helped others with and gathered thru intense reading :)
This is a "version" 2 of a previous post.
Check out the old post for some of the questions :)

Video, Decoding, audio, spdif:
1)
Divx/Xvid (and about everything else) thumbnails and playing:
http://ffdshow-tryout.sourceforge.net/
This is the only codec you need for ALL media except h.264 and mpeg2 hardware.

During installation don't touch much. During setup it will ask you about mixer settings (speakers). Tell it to leave mixer off for SPDIF(toslink/coax) or select your speaker configuration from the list (do not select mixer if you use SPDIF passthru).

SP-DIF setup:

The final screen - tell it to open Audio configuration.
Select the [Codecs] (to the left - one of the first) - at the items AC3 and DTS - change it to SPDIF for both if you wish to have divx, xvid, mkv, mpg4 etc. to stream HD-Audio it to your receiver thru SPDIF. This is only possible if you have selected your SP-dif interface as your preferred in Vista (in some hardware configurations you need to disable Speakers!)

For HD/SD Digital Audio be sure to:
Start, Control Panel, Sound, Right Click SPIDIF Interface, Properties, Advanced(tab), and then.....
UNCHECK "Allow applications to take exclusive control of this device"
This will allow you to Record HD and Watch another channel without audio stuttering

Don't install any codec packs, Gordian, kmedia, ultimate etc....Don't!
Don't install Nero Burning Rom - it's f*** about everything up (march 2007) - including ordinary thumbnails etc.

2)
MKV AND TS With matroska
h.264 codec incl. thumbnails in vista and integration with VMC:
Download Haali Media splitter : http://haali.cs.msu.ru/mkv/MatroskaSplitter.exe
Just leave the defaults on in the installation screen - make sure "explorer integration" is selected - this enables thumbnails.
For TS and PS MPEG files - add the selections in the install dialog

Enabling ts and mkv files in VMC and Mediaplayer do the following:
Open notepad and paste the following in:

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.mkv]
@="MatroskaVideo"
"PerceivedType"="video"
"Content Type"="video/x-matroska"

[HKEY_CLASSES_ROOT\.ts]
@="MatroskaVideo"
"PerceivedType"="video"
"Content Type"="video/x-matroska"

Save the file as : matroska.reg to the desktop afterwards doubleclick it and say YES to add it to the registry.
You can now see and play TS and MKV files in VMC

MKV AND TS With Matroska and CoreAVC (the best!! but not free)
Use together with ffdshow (with h.264 disabled in Video configuration)
The same as above but add the following instead:

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\.mkv]
@="CoreMedia.MKV"
"PerceivedType"="video"

[HKEY_CLASSES_ROOT\.ts]
@="MatroskaVideo"
"PerceivedType"="video"
"Content Type"="video/x-matroska"

Save the file as : matroskaCore.reg to the desktop afterwards doubleclick it and say YES to add it to the registry.
You can now see and play TS and MKV files in VMC

3)
MPEG2 codec
Use PowerDVD 7.2 og 7.0 - this is the best.
Open PowerDVD and go in to setup/config (the tools button) - select hardware optimized. (it'll work for some and not for others)
Close powerdvd.
Setup MediaCenter with correct mpeg2 codecs with this tool:
http://www.whittakermoore.com/VMCD.exe
Select PowerDVD7 for Video and Microsoft DD for Audio.

If your MPEG2 playback begins to behave strange/stutter etc. It sometimes helps to:
Open VMCD.exe select MS MPEG video and Audio for MediaCenter - close the application.
Open MediaCenter - select LiveTV - Close MediaCenter again.
Open VMCD.exe and select PowerDVD7 as the Video decoder again and MS DD audio.

For ATI users with Catalyst Control Center - Make sure that AVIVO settings is set to BOB (not auto/Weave etc.)

MEDIA in VISTA:
1) Adding videos to VistaMC
Place shortcuts to your content folders (mkv, avi, divx, xvid) - the shortcuts should be placed in Shared Folders -> Videos. You can name the ShortCuts anything you want.
Divx files shouldn't be named MYMOVIE.DIVX - but MYMOVIE.AVI

2) If you have a lot of "Self created" folder.jpg's for you music - make sure they are marked as hidden before adding music/pictures to your WMP library.

3) Stuck with Folders that keep appearing:
Open your Media Player - navigate to Library - select Folders (little triangle pointing down) and remove those that annoy you.
Before deleting - make sure only to delete from library not from the filesystem (Functions -> Settings -> Library -> Do not delete from filesystem when deleting).

4) Adding DVD's
Enable DVD library with this key:
HKEY_Current_user->Software->Microsoft->Windows>CurrentVersion->MediaCenter->Settings->DVDSettings->ShowGallery
Set it to Gallery (with capital G) instead of Play
Remember - one folder with folders within for each movie. Within a movie folder the folders VIDEO_TS and AUDIO_TS is placed.

Or make a .reg file as mentioned above with this:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\DvdSettings]
"ShowGallery"="Gallery"

Add DVD's like you add music - from within WMP.
Do not blindly add folders. Make a good hierarchy with a folder structure like:
d:\DVDs\Mymovie\Video_TS
d:\DVDs\MyMovie2\Video_ts

The DVD files within the Video_ts folder should match the content of the original DVD (video_ts.bup, video_ts.vob, video_ts.ifo etc.)
If you RIP and SHRINK DVDs then make sure to rip all files not just streams.

5)
Adding media to Media Center:
Don't just add everything, folders, music etc.
Use the correct tools.
Use Media Player's library function to tell where to look for music, pictures and DVD's

6)
DVD library "more info" function.
DVD's can be looked up in a central Database if the Correct ID is placed
For correct ID's - look them up on www.dvdxml.com and save the XML file like this:
the_faculty.dvdid.xml placed within the movie folder - not in the VIDEO_TS folder.

LIVE TV Quality Trouble:
1)
Change BitRate:
First of all check the key:
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Media Center\Service\Video\Tuners\DVR] and find the KEY DefAvgBitRate
Change it to somewhere between: 20000000 and 90000000
Select DECIMAL VALUE when changing.

REMOTE DESKTOP (multi users and blank password)
1)
(THANK YOU SCUFFS!!!!)
Download this: http://mjwii.com/prog/termsrv.zip
Unzip to c:\termserv go into this folder and make a shortcut to termhack.bat (right click drag to a place and select create shortcut here)
Right-click on the shortcut and select Properties - in the "Destination" add the following:
C:\termserv\termhack.bat MULTI BLANK
Only set BLANK if on a local-private network. BLANK enables passwordless connections.
If you use a non english version of Vista:
You need to know what the Administrators group is called in your language. Edit the termhack.bat file and go to the line that says:
icacls %SystemRoot%\System32\termsrv.dll /Grant Administrators:F
And change [Administrators] to your language.

NOW:
Right-click and select "run as administrator" on the shortcut

Now create users on your VMC and connect with these - Do not connect with the one you use as the default for TV/Video in your livingroom.

Various:

1)
For editing and backup of ones channels and order they come
The file:
C:\ProgramData\Microsoft\ehome\EPG\prefs\prefs.xml
Open it with notepad.
This file holds everything about your channel, frequency, name, Virtual name etc.
It's a good thing to back this up - if you ever reinstall Vista

2)
Recording configuration is stored here:
C:\ProgramData\MicroSoft\ehome\Recording\Recordings.xml
There is a backup there - but it's nice to copy it to another place :)

3)
Some of the following items require you to enable visibility of hidden folders and OS folders
This is done thru Control Panel -> Folder settings

---------
If any of the above things doesn't work for you - you probably misspelled something - or you went ahead and started installing things - without cleansing your Vista.
Vista x64 is unknown and explored  - try some of the stuff.
Vista 32bit all of the above works.

Remove every program you have installed, that has to do with:
Codecpacks
Nero burning.
Several MPEG2 codecs you have tried.

Make sure your Media Center works before you start - i.e. Media Center, TV, tuning etc. must work with standard Vista Codecs before you start out.
Get ALL updates from Microsoft!

I hope it helps some of you guys/girls :)

Thanks, zosoDK.  I assume this is the old post to which you refer?

Yesssss :)
The author seems to be the same - actually - some of it I really can't remember writing :)

Looks great!  I vote for a sticky.  However, if you want the BLANK passwords to work, you would need to double-click on the newly created shortcut to the hack BAT file, and not on the BAT file itself. 

Conversely, there is a security policy setting that can modified for allowing blank passwords on a private network via RDP.  However, this setting is found only in Ultimate, as Home Premium does not have a security policy plug-in. 

What I don't understand is why you recommend using a different user account to administer via RDP from the account that normally runs the Media Center in the living room....  I find it easier to modify settings that directly apply to the account that runs VMC. 

Also, by shared folder, I assume you mean the "public" folders in Vista?  Why would it necessary to put shortcuts in there?

Actually - if you wanna do things while somebody is watching TV.
I have really bad experiences with connecting while my wife is watching some show :)

The proper way is right-clicking and run-as-administrator on the shortcut. Did i really write something else(?). I ment what i just wrote - if it says something different, then i stand corrected :)

And yes, I hope it eventually will end up as a sticky - perhaps when it is more complete.
But a lot of peope keeps asking the same questions over and over again. This might be because the [search] field on TGB searches globally and not the Current forum people are visiting/browsing.

I am 100% sure of the lists answers and solutions - no doubt. Sadly they don't offer any good solutions and answers for 64bit users. They are pretty much stuck right now.

Everything you have mentions just works straight off for me, I installed the Vista x64 Codec Pack that i found by googling and i have everything i need. Whole thing works a charm.

1) Adding videos to VistaMC
Place shortcuts to your content folders (mkv, avi, divx, xvid) - the shortcuts should be placed in Shared Folders -> Videos. You can name the ShortCuts anything you want.

OK, just to clear up any ambiguities here:  According to the above, if I have 2 folders of videos that need to be added to VMC, I make 2 shortcuts - one for each folder and stick the shortcuts in [C:\users\Public\Public Videos], correct?  This seems a bit odd, but if it works, heh....  By "Shared", I think you mean the default shared Public directories. 

Adding media to Media Center:
Don't just add everything, folders, music etc.
Use the correct tools.
Use Media Player's library function to tell where to look for music, pictures and DVD's

Now, did you intentionally leave out Videos here, because it works better to make shortcuts of video folders with Explorer and use VMC's library function for all *other* media (pics and music)? 

I seem to have continually monitored video folders despite having removed the folders from both VMC's library and WMP11's monitored folders. 

Yes, quite intentionally :)

It works best with only pictures, music and DVD's
Even though that gives a bit of a headache - because of the folder.jpg's that shows up in pictures.
Unless they are hidden

Great news :)

That means that there's still hope for 64bit :)
A lot of people are having trouble with 64bit...any links for the Vista 64bit codec pack?

Hey, here is the link to the thread, it's on MSFN forums. It's working a charm for me so good luck with it people. Please make sure you download the correct architecture, no one but god can help you if you can't do that right

http://www.msfn.org/board/index.php?showtopic=66826

If it works as well for others as I, maybe someone could look into having it put on (y)our download page, here at TGB.

>>Use PowerDVD 7.2 og 7.0 - this is the best.

Which MPEG2 decoders have you tried in Vista?

They have the same Decoder (PDVD7)

I'm sure the comment on PowerDVD7 and 7.02 meant that the earlier one was simply a better piece of software to use and not related to how well they decode.

I was asking if you have tried decoders other than PDVD.

Correctamundo :)

It's based on compatibility and HW decoding.

People with AMD CPU's seem to have HW support thru PDVD7 and Intel is about 50/50.

The quality issues between cyberlink, intervideo, nvidia etc. is not an issue here.

It's just an observation, software compatibility with Vista, integration with mediacenter.
Cyberlink seems to lead the field here (right now)