Yup, same here, demo reboots my PC after a few minutes of play on the Jump track, and after a few seconds of the 1st and 2nd tracks (racing with AI).
I'm using the 66.77 WHQ drivers with a TI4600, so I can confirm it doesn't work with these drivers either, at least not for me. Hopefully they'll fix it because like a lot of people, I've been anxiously awaiting this game, but this isn't a good way of selling me on it.