On my system, X wouldn't start at all, because of not loading the fglrx module. Manually loading it solved the problem.
But then, another problem came. Games don't work, graphics go completely scrambled, like a stairstep effect or something, but OpenGL screensavers work great though.
I guess, I'll just have to wait for ATI to release their drivers, because these driver's can't be the final versions...back to the original XFree drivers, and everything works great.