If you're going with a 64 bit proccesor, I cannot stress enough that you should go with a 939 socket as opposed to a 754, a bit more expensive perhaps, but it has far better performance and leaves the door open for upgrades in the future.
Also, even if you aren't comfortable building your own computer, for a small fee you can pick out your parts and have someone working at the store do it for you.
Intel C2D E6320 / AMD Athlon X2 3800+
Gigabyte 965P DS3 / DFI nF4 Ultra-D
2GB OCZ Gold PC2-6400 / 2GB OCZ Gold PC4000
eVGA 8800GTS 320MB / eVGA 6800GS 256MB
150GB Raptor / 74GB Raptor
2x500GB / 320GB
OCZ GameXStreme 850w / OCZ StealthXStream 600w