Perhaps you can tell us what is your hidef system specs, including your HDTV, receivers, and PC? And where are they located?
I have a dedicated PC that I use to watch my high def movies on the HDTV across the room. I bought a 35foot HDMI cable to connect my PC and HDTV and they work great, except that I can't enjoy the lossless HD sound since I am connecting the audio via opticals from my motherboard.
There are also some other options, ie streaming wirelessly from your PC to a media center (or PS3 if you own one).