Video card sick - how to restore onboard card

Hello,

I have a Sony Viao which came with an onboard video card. Replaced it with an Invdia GeForce 4mx 440 a few years ago so my kid could play Tony Hawk. The video card seems to be going bad now -- screen keeps getting all goofy on me, blinks on and off, locks up, etc. I don't mind buying a new card, but since my son doesn't play games on my pc anymore I'm thinking I could just switch back to the onboard graphics. When I go to device manager in windows it only lists the GeForce card, so I can't just switch back to the onboard graphics. What steps do I take to disable the GeForce and re-enable the onboard graphics?

thanks!