If your card is a geforce card, then you should be running the detonator drivers. Download and install the current driver from nvidia.com or go to
www.guru3d.com and try any number of beta nvidia drivers there. The 28.80 driver is very good and I'm running the newest 29.42 driver.
If you're running win98 change to a default vga adapter after downloading a detonator driver. Then install the new driver. In winxp, uninstall the driver and then install new driver. Make sure anti-virus is disabled when installing the new drivers. I think this may very well cure your problem.