Well, if you're just running a game system that should be fine..But if you're playing CSS or BF2 with more than 20 players most of the time I would actualy build a custom one.
It's cheaper, my computer i'm running right now has these specs.
Video card : X-tasy radeon 9600 256 MB
Ram : 512
Hard drive : maxtor 120 gig 7200 RPM
Motherboard : Asus K8V-SE deluxe
CPU : X86 authentic AMD ~ 2002MHz
Without the case, and other accescories it came to 1300$, order things ofline and you get better deals.
*caugh* newegg.com