So this is not a big deal.
Check out
http://www.ati.com
Drivers & Software ---> Linux Display Drivers and Software ---> under Linux x86
Motherboards with ATI Graphics ---> ATI Proprietary Linux x86 Display Drivers for XFREE86 / X. Org Version 8.28.8
Just use the they steps described there.
In order to get only a working screen for the suppose of doing what I ATI tells you to do out of your linux system. You can attempt to create a standard xorg.conf
Try "system-config-display" command as root
choose a standard lcd panel 1024x768 and vesa video card.
After you downloaded all the files from ati and after you done all the steps they recommend you will have a nice desktop with fine graphics.
But don't spend so much time to find the correct monitor use the closed to it's specifiations