^This. RabbitGT had a good idea with the to 6850's but with a budget, you should buy a board with 2 or more pcie slots, a decent power supply, and the single most expensive GPU that you can afford. This will give you nice initial performance and some nice headroom for an upgrade down the line by crossfiring/SLI then.
As far as the Processor, I'd recommend the Phenom 955 with a cooler master hyper 212+ and some MX-2 thermal compound. It'll set you up to overclock when you want to. If you dont want to right away, atleast get the 955 and stock cooling.
For the motherboard, look for a gigabyte or an ASUS board (make sure the ASUS is not EVO) with 2+ pcie slots. The specs will leave you a solid rig and a lot of head room for budget upgrades with big performance increases down the line.Edited by fordy314 - 2/13/11 at 6:16pm