go with batchuka's build but with an intel Q9550 and ddr2 motherboard with ddr2 ram since they are better at multi-threaded apps.
@OP: if you prefer the Q9550, I'd recommend a GA-EP45-UD3P motherboard. It will work well with the two HD 4770 cards.
RAM for it: http://www.newegg.com/Product/Product.aspx?Item=N82E16820231209
If you're the kind of guy who just uses a PC for 7 years and then throws it out, then by all means do this.
Batuchka's setup is easier to upgrade. Let's say in 2011 both AMD and Intel come up with a $300 CPU that is WAY faster than the Q9550 or the Phenom II 955. That's very likely IMO. With batuchka's idea, you'll be able to spend $300 and get the new CPU and keep the MB and RAM you already have. With the Q9550, the upgrade will cost about $500 and a bit more effort because you'd need to replace the MB and RAM too.