Actually, if all you did was run the RPM, then I don't believe anything was installed.
All that happened was the module and/or code to build modules were placed in /lib/modules
Here's watcha do -- as root
That's that. Next step is to change your /etc/X11/XF86Config (may end in -4)
Change the driver line from whatever it is (probably vesa, ati, or radeon) to fglrx.
Make sure the default color depth is set to 24. Instead of 32 or 16.
That should be all you need to do.
NOTE: to build the modules above, you need to have your kernel sources installed at /usr/src/linux. And they need to match your running kernel :-D I'm relatively sure that the source isn't there by default in Red Hat... You may need to find out how to get the source for your modified / patched Red Hat kernel.