I also experience the same problem.
Intel Pentium D 940
Intel 945GPM
1GB RAM
nVidia 6600
Something else you might look at is the power options on your Vista PC. Click the advanced button and go through the drop down tabs, there's one that disables the PC going into standby (screen, disks and power) when you are streaming. This might help.
Cheers
i've been experiencing the same problem with Vista RTM to an XBox 360.
UPDATE the registry hack ended up working for me.
If you have ATI hardware, check out the latest drivers released today.
cheerio
Howard
I doubt we'll see anymore Media Center specific video drivers since it's built into the Vista sku now, try out the latest Vista drivers and see what that does for ya.
I got sick of all the ATI driver issues I've been having so I moved all my machines over to Nvidia and haven't had any video issues since.