Please take a look at the following device:

Blonder Tongue Laboratories HDMI-to-QAM Encoder

Would it be possible (albeit quite expensive) to encode your own source (cable box, sat box, blu-ray, etc) in HD to QAM and then have Vista Media Center receive that signal with a QAM compatible HD tuner? Thanks in advance!

Best,
Matt

that might be possible to do, but seriously....at what expense

Sometimes cost is no option...just functionality.

I have wondered why a device like this hasn't come out. Something that would take in an HDMI of Component input and the output it into ATSC for use with Media Center (Media Center doesn't natively support QAM that this device does).

Well, you could "probably" pull it off.  An HD Homerun should find the QAM signal whenever it does a scan.  But how would you make MCE change the channel on your Cable Box/Sat Box without also changing the channel that MCE is displaying?  Seems like you would have better luck buying one of those multi thousand dollar professional HDMI capture cards that can handle HDCP and using that for video input, and then using an IR Blaster to change the channel for you.

I have read a few posts where people have mentioned stuff like that.  There is a company called Blackmagic that makes an HDMI capture card, but it isnt HDCP and I think that the end of the thread talked about no vista support as a capture card through MCE.

If there was a way to capture the HDMI output of a cable/sat box, and control the box via RS-232 or Firewire I'd be all over it, but as many times as someone has asked the question, no one has had a solution.