It depends on the kernel you have and the ATI driver you are using.
Post the follow output from these commnads
If using 8.42.3 there are problems under the 2.6.23 kernel tree. AMD/ATI is working on the driver to improve on the next release. The projection is later this month. But there is only so many hours in a day so it will take time. The kernel made some changes which require rewrite of the drivers.
The only way to get say compiz-fusion to work is using kernel 2.6.22 and the ATI driver of 8.40.4. This is what I have going to support DRI and 3D. I do have the 8.40.4 working on kernel 126.96.36.199 but requires patching and rebuilding of the x11-ati-drv-8.40.4 rpm to make it work. No changes require under 2.6.22 kernel tree.
Several post discuss this subject so I would check them out as well.
Distribution: RHEL 5.1 with Pieces of this and that.
Kernel 188.8.131.52, KDE 3.5.8 and KDE 4.0 beta, Plus Development src.rpm, ATI fglrx64_7_1_0-8.433-1 rpm with 3D and DRI working.
Acer 5100-5840 with webcam, ati, sdcard reader, sound, atheros based wireless, all working. Only thing not working is the memory stick reader.