I finally managed to build the rpm packages here on my Fedora 8 using modified scripts from phorogit.
Now I've installed them, loaded the fglrx module, restarted X with the same working xorg.conf I had before and the result of $fglrxinfo is
I suspect something went wrong, but I really can't figure it out... I rebuilt-reinstalled the rpms but it didn't help.
display: :0.0 screen: 0
OpenGL vendor string: Mesa project: http://www.mesa3d.org
OpenGL renderer string: Mesa GLX Indirect
OpenGL version string: 1.4 (2.1 Mesa 7.0.1)