I think you need to instal/uninstall/reinstall the drivers to change between them. I originally got the Geforce as I wanted to try RTW, and first installed the drivers on the CD provided - that wasn't good enough, so upgraded to 79.xx or 81.xx I forget which, but that killed MTW functionality. After that I got bored with RTW pretty fast, so just uninstalled the new drivers and went back to the even older ones bundled in with my OS (51.xx, I think) and that is just fine for MTW. You might be able to do something clever with hardware profiles, but I'm not the one to advise you on that, I'm afraid....