You should check out what card you have... also read the minimum spec on the back of the box... I find that the best make of graphics cards are ATI - personally i have a radeon pro... you can get all sizes from 32mb to something stupid like 512!
The cache on your PC helps as well, see what amount of RAM you have, whether itd DDR or SDR etc, and also upgrade to DX9.0b:
http://www.microsoft.com/windows/directx/default.aspxGood Luck!