I currently have the following HTPC setup for the home theater:
AMD X3 720 BE (unlocked to X4)
2x Sapphire AMD Radeon 4850s crossfired (I believe they are each 512 mb memory)
Corsair 650W PSU
One of the most annoying problems that I have is that I cannot leave the HTPC on. If the HTPC is already on when I turn on the projector I get "popping" noises (almost like fireworks). I am guessing that maybe it has something to do with the 4850 cards because that doesn't happen on any other A/V device that I have. And it happens with any A/V receiver. I used to have a Pioneer A/V receiver and I got the exact same popping sounds as soon as I would switch over to the HTPC. I always have to turn on the projector first and then the PC to avoid getting the popping noise.