I did a fresh install of the newest RHEL5B2 nightly snapshot on my ThinkPad X32 with ATI graphics. Compiz does not work and investigation shows that the radeon kernel module is not loaded and thus DRI is not available. I tried loading the module manually but that does not help. On a T42 with Radeon M7 everything works.
Created attachment 140893 [details] Xorg.0.log
We don't support DRI on RV100 since it's known to be unstable. From Xorg.0.log: (II) RADEON(0): Direct rendering unstable on RV100, disabling