Well here are the requirements for the game:
Min: XP SP2 or Win2000; Intel P4 2ghz/AMD xp 2200+; 512mb ram; 128mb nVidia 5700/radeon 9600; directx9.0c
Recommended: Intel Core 2 Duo E6400/AMD athlon 64 X2 4200+; 1Gb ram or more; 256mb directx 9.0c nVidia 7900/radeon X1850
So I would guess that you would need a more ram and a faster CPU.
It is one EXTREMELY hungry game!