I would seriously consider replacing your graphics card at this point. I doubt that this is an issue caused specifically by The Sims 2 ... If you can take your computer back to the place your purchased it (if still under warranty) or find a reputable computer dealer in your area to service it, I would recommend doing that. From your error messages posted here I would suspect a faulty graphic card (seeing as you already updated your drivers).
please do double check the temps first. with both my eperience and what other people have suggested, that seems to be the culprit. and while temp may be cool now, it doesnt take much to jump to extreme temps when your running an intensive game. also, double check for dust and whatnot.
I think his problem IS the Video Card. The Geforce 6200 is specifically designed for bargain /barebones/ gaming. It utilizes all the modern technology of the Geforce 6 series, but lacks all the pixel pipes and video ram. It was essentialy the card that allowed people to at least play Half Life 2 at lowest settings.