San Andreas Lag , GeForce 7600GT Urgent

Hi,
I/m experiencing problems with GTA san andreas.......The Game Lags......With a Nvidia GeForce 7600GT which is a 256mb card with shader model 3.0. I dont know why, I have the same problem with other games. GTA San Andreas works with no lags on my other computer which has 128mb onboad graphics card.

please help


My Config is:

Intel Celeron 64 2.66GHz
Nvidia GeForce 7600GT
1.5GB of RAM
Windows XP Service Pack 3