VERY IMPORTANT! Ensure that Windows XP has Service Pack 2 (or better) or that Windows Vista has Service Pack 1 (or better).
Minimum System Requirements:
Operating System: Windows XP (with SP2) or Windows Vista (with SP1)
Processor: 3 Ghz Intel
Pentium
D 830, AMD Athlon
64 X2 3800+ or better
RAM: 1 GB Windows XP / 2 GB Windows Vista, Windows 7
Video
card: NVidia 6800 or ATI X1650 or better, 256 MB DirectX 10.0–compliant
video card or DirectX 9.0c–compliant card with Shader Model 3.0 or
higher.
Hard Drive Space: 1.5 GB
Sound: DirectX 9.0c Compatible Sound Card with Latest Drivers
Internet: Broadband connection and service required for multiplayer mode
Windows-compatible mouse required
Recommended System Requirements
Operating System: Windows XP (with SP2), Windows Vista
(with SP1) or Windows 7
Processor: Intel Core 2 Duo Family, AMD Athlon 64 X2 5200+, AMD Phenom or better
RAM: 2 GB
Video card: NVidia 8600 GTS or better, ATI X1900 or better, 512 MB of graphic memory
Hard Drive Space: 1.5 GB
Sound: DirectX 9.0c Compatible Sound Card 5.1 with Latest Drivers
Internet: Broadband connection and service required for multiplayer mode
http://www.bigdownload.com/games/james-camerons-avatar-the-game/pc/james-camerons-avatar-the-game-demo/