You probably need to run "fglrxconfig" to generate a proper XF86Conf-4 or xorg.conf file. (Depending on whether you are running XFree86 or Xorg)...
On my system (gentoo) this is located in: /opt/ati/bin/fglrxconfig
Remember, you will need to know your monitor's horizontal and vertical sync rates before you do this!
Also, on my system I have to run "opengl-update ati" afterwards to switch to the ATI OpenGL implementation (but I think this is a Gentoo thing....)