You can have 2 option:
- Download the newest driver
for your nVIDIA card, use the Un-install feature of the soft to remove the current driver then re-install.
- Use a clearly uninstall program, I suggest to use Your Uninstaller Pro 2008. You can find this software at 9down.com.
I have use these way for my nVIDIA 8600M GT and also my Ati Radeon Mobility 3670, both working well. Hope it good for you too.