Installed graphic card driver and now no video

[cmaceWI]

I did something stupid. I installed a video driver and after I rebooted, I have no video. How do I uninstall the "bad" driver now? How can I get back my video? CAn I put another card in and get it to run. The on-board video slot is broken. It is a PCI slot and I have the NVidia MX 4000 graphic card. HELP!!!!!