The folks at NVIDIA have released a new beta-driver package, Forceware 180.84, specifically optimized for use in Grand Theft Auto 4 on PC.
Improvement in frames per second varies from just a few to over 10. More than enough to give these drivers a try if you feel GTA4's performance is letting you down.
Head on over to www.nzone.com and grab your driver package. Be sure to share your results in our forums!