:s If you save up 100$ more, then you could get a pretty decent system.
MSI K8N Neo4-F pci-e 85$
6600GT Pci-e 100-140$
amd 3000 socket 939 venice core - 140$
1Gb valueselect or something - 70-80$
Case (you choose) - 40$
Powersupply - fps 450w - 50$
dvd rom optical drive - 25$
western digital sata 80gb harddrive 7200 rpm 8mb cache - 60$
soundblaster live! soundcard - 30$
extras - 50$ (like keyboard, cables, mouse, etc.)
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655$
if you don't need it, take out the extras or downgrade the ram to try to fit under 600$.
Note these prices are estimates and shipping would be added on to the final price