Hey - if you're running XP and your game performance stinks, despite massive amounts of RAM, try disabling 3D Sound. I was having bad perf problems with XWing Alliance, and disabling 3D sound worked like a dream! My specs are:
PIII 600MhZ (slot 1)
15 GB HD
512 MB Ram PC 100
XP Professional
SB Live X-Gamer
Radeon 7000
Thrustmaster HOTAS Cougar