The best computer you can get for the money is the one you build yourself. You can build a good AH compatible game computer for less than $600.
Current stable;
AH computer; Antec 900 case, Asus M2n Deluxe SLI, 3.2Ghz AMDx2 chip, 2GB Ram, 8800GTS VC, 150GB Raptor 10k HD, Creative labs sound card, 750 watt PSU, CH Products Joy,Throttle, Pedals, 24 inch Samsung Monitor
Backup(gaming,video editing); Full tower case(w 2-250mm Fans), XFI MB, Q6600 2.4Mhz chip, 4GB Ram,
2-8800GTX VC, Creative Labs Sound Card, 2-150GB Raptor 10k HDs (Raid O) 1-40 WD HD 7.2k, 1000 Watt PSU, Water Cooled.