We got a new PC with Media Centre through morag's work,
(Just before Gordon Brown pulled the plug on the tax free deal:tosser: )
We had it installed for us and the tv works fine. We haven't tried Sky through it, just a bog standard council tv ariel. Were getting about 70 channels including radio.
To set up ( on ours anyway) turn on media centre/ go to settings/ TV / Set up for tv signal and follow the instructions from there.
Once you get it going, Run a scan for more services about once a week, there are always new ones coming up, and some get delisted.
Just in case, ensure the tv ariel is plugged into the tv card thingy(obviously)
Check that the tv card is working correctly and the drivers are installed properly.
Hpe you get it sorted.