I just completed a new build for around $500 that runs Bioshock on High at 1280 x 1024 (which was my goal). Anyways, I ordered the hardware a week ago, got all of it 2-3 days ago, and am now up and running in Vista. Everything has gone very smooth in part due to the tips and advice I picked up here.
Athlon DC 4800+
Gigabyte microATX GA-MA69VM-S2
A-Data 2 x 1 Gb DDR800
512Mb DDR3 Radeon 3850HD PCI Express x16
Antec Sonata III case with two variable speed 120mm cooling fans
500W Antec Earthwatts PSU
Seagate 250 Gb 16Mb Cache SATA drive
LG DVD burner IDE
Comments: Although it has been said many times, the Radeon HD3850 is a frikkin' HUGE card. It fits, barely, in the Sonata case after I added an optional front 120mm fan. No grounding problems with the Sonata case as has been discussed here. The Gigabyte mobo has been very nice and stable, I just wish I wouldn't have lost one of the only two PCI slots on the board. I knew it going in, but I felt it was still the best option for the price point ~$65. Wish they would start considering these large video cards when they design these mobos.