Maybe that Registry edit is what is causing this issue then? Maybe a full uninstall of the game and then reinstalling it to the correct directory would have been better?
That is the only thing i can think of. Unless the drivers themselves are unstable. But you would only know that by check the AMD/ATi site.
It is a well known fact that ATi and Vista do not play along nicely yet. Of course the Vista page doesnt show up. I would contact ATi.
Cheers,
Mak