If you´re familar with driver installation/deinstallation
try out the some older version. (like 66.93 or earlier)
newer drivers are mostly optimized for latest cards
(like nvidia 6600 or even those 7800 monsters)
Maybe an older one is better for your card.
But please don´t blame me for wrecking your system,
it´s always possible something goes wrong with that
driver stuff. If you´re XP user set a system restore point
before touching the system.
Also possible the error has nothing todo with the VGA driver at all.
Do you can tell your current driver version?