Oh, so you really do need to uninstall drivers then. I'll be all set for a while.
For ATI cards, I have always had good luck just uninstalling through control panel. Although using a driver cleaner after that is a good idea. For NV cards, I use control panel first and then detonator destroyer and/or other cleaners to get rid of them there nasties left behind.
SOme people will say to do a clean OS install. While you might gain a tiny percentage of performance doing this, it probably won't be needed. Only time I ever needed a OS reinstall was when trying to switch from MSI Nvidea drivers. For some reason those never uninstalled properly.
ABIT IS7, P4 2.6C, 1GB Corsair XMS 4000 Pro Series, Radeon 9800 Pro, Santa Cruz, TruePower 430watt