Socket 939 is only a couple of bucks more than socket 754, plus I'm not sure how many (if any) socket 754 boards support PCIe which would be a vital addition to any gamer.
Regardless though, I would recommend...
AMD Athlon 64 3200+
MSI nforce 4 socket 939
The rest isn't too important, those are your basic components that will matter the most performance wise.
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