Don't run the game at higher than 1024x768 (800x600 is probably the best for that card), set the texture size to 256 (or lower).
If you have 512MB of system ram, then make sure you have the 'preload textures to system ram' option checked in the video setup for the game.
Set the slider for the object distance to 1 mile.
In the ATI control panel, under the D3D tab, set the slider all the way to performance.
The 8500 is a very old card and is not a fast one. It will load down pretty quickly, depending on what CPU you have. I have one in this very system I use everyday. And with an 800Mhz P3. It will bog down in large traffic areas.
Above all, your system must be very clean of any and all background processes. That card will need all the help it can get if you are running less than a 2Ghz CPU.
There are no generic settings we can post for any specific video card. There are far too many other variables which go into the performance of a system.
