Distortion Effects

[Voodoo]

The game runs great on my machine, but only if I turn off Distortion effects. I'm unsure of why I get such a FPS hit when they are turned on. When Distortion turned off, I get very high frames. Any idea what might be causing this? I'm also running the newest nVidia beta driver...

My Machine
AMD Athlon64 X2 3800+
2GB RAM
2x 7600GT 256MB in SLI

Thanks!