The problem is that at the moment buying something will get you superseeded in a months time. And when these guys saw your budget, they just wanted the best for you - but as it's not their PC, they might say wait a year until quad core CPUs come out.
Personally, I would say go AM2. It'll be relatively future proofed, and you could get a really nice dual core
To go with that, grab something like the Asus M2N32-SLI-DLX, which is a really nice motherboard, and 2GB of low latency DDR2 RAM.
Next, grab a 7900GTX - you can then add one of these later if you feel like it.
Finally, a single Western Digital Raptor X along with a 250GB Samsung Spinpoint P120S, a decent 500W+ PSU, and any case which takes your fancy, along with a DVD writer such as the Pioneer DVR-111DBK and, if you've got anything left, a Creative X-Fi sound card.