Could you tell the settings you use in the sim?
Also check your drivers and driversettings.
And if all that doesn't help, some BIOS-tweaks might be needed, allthough I wouldn't recommend those if you don't know exactly what you are doing.
My Comp is tweaked for best performance. I have a stripped Version of Win98SE (with parts of Win 95) for high Windows-performance, I got smaller cycles in the bios and a lot of other stuff. I found that I can compete with more expensive card/cpu/OS combinations by doing all that.
BTW: I run at 1024*768, 32bit, medium quality. I get 23fps when sitting high in the corner looking at the complete city. On ride FPS don't go below 35-40.
Buster.
PS: To find out what driver the sim is using, start the simulator and click on "INFO". At the bottom it will tell you which OpenGL-driver is being used. That should be:
NVIDIA - MX,AGP,SSE,3DNOW! - Version 1.4.1