This game runs fine on my P4 3.4, MR9700, 1G laptop, so you shouldn't have any problems with it. If you're using a 5700, you need to use AW drivers. I've read that other drivers cause issues with the platform and the 6800 go.
If it's a 7700, make sure the game is patched to the latest version, and you have the latest drivers. You might try removing the old drivers with a driver cleaner, and doing a fresh install of the drivers...
You can also go to the GTA website. There's lots of help there if this is the only program you're having issues with.