try $Pref::Input::MouseInvertYAxis = 0;
Thats what I had seen posted, but it didn't make any sense to me, since the value was a 0. I guess it has to be 0, and not 1? *shrug* The problem may also be that I had a space in there. So try it with the 1 and no space and the 0 in both, I guess. Beta forums should be able to tell you for sure.