I had this problem after installing the official ATI drivers, too. It did that no matter what I did/how I installed the drivers, but I found that when using the livna.org ATI drivers, it all works fine. I get full 3D acceleration and it logs out just fine now!
I've got the instuctions of how I installed it here: http://forums.fedoraforum.org/forum/...6&postcount=40
Try that and see if it works.