I'm no expert, but i'll try. I have an ATI card so i can't help you exactly but the ideas should be the same.
-The obvious one, turn down your graphics settings and see if that helps.
-Uninstall your old drivers before updating. NVidia might have a special tool for it on their website (ATI does for their drivers)
-Make sure your NVidia preferences (in Windows) aren't trying to override an in-game setting. There should be some settings where you can select texture filtering and stuff like that, make sure everything is on "Application Default" or something similar.
-I doubt this is it, but if you unpacked your M2TW files make sure you deleted the 2 "new_desc_geography" files.