[Update: ATI open sourced the fglrx drivers, which is why this step is not necessary]
As of RHEL5 kernel version 2.6.18-128.1.6 (Apr 30 2009), Red Hat has inproved their kernel and default ATI drivers to the point where it is no longer necessary, as far as I know, to install ATI’s own drivers. This should now be considered an optional part of the install.
I have removed the ATI drivers from the astronet machines, because they are no longer worth the SELinux and kernel update hassel. To remove the drivers from machines that originally had them, I used these commands:
#>rm -rf /etc/X11/xorg.conf
#>cp /etc/X11/xorg.conf.original-0 /etc/X11/xorg.conf
#>yum -y reinstall xorg* mesa* gnome-screensaver kernel-headers
#>reboot
This should (1) Prevent the kernel and xorg from trying to load the 3rd party driver module and (2) Replace any ATI-compiled xorg and/or rendering libraries with the official Red Hat ones…which are, finally, good.