-Semprons/single core Athlons (which is it?) aren't the greatest gaming processors. Newer games and video card drivers take advantage of dual-core CPUs. Try for a cheap Athlon 64 X2 processor.
-The 8500GT is more of an HTPC card than it is a gaming card. You'll need an 8600GT for barely acceptable performance, but you'll want an HD3850 or 9600GT for buttery smoothness at higher resolutions. The 9600GT was recently selling for just $99 (I believe this was at Tiger Direct).
-You'll want a larger hard drive. I downloaded Unreal Tournament 3 a few nights ago, which gobbled up 9GB of space. Aim for at least 250GB. Hard drives are cheap! A 250 probably wouldn't cost much more than an 80.
-Everything else looks acceptable for a budget gaming system. While a chipset by DAAMIT or NVIDIA would be nice, it is not a must, unlike the other upgrades I've mentioned.
The creme de la creme of Socket 939:
Opty 185 @ 3.2GHz
SLI'ed GTS-640s, both flashed to 625/1458/1950