I wonder what driver you are using now, is your chip know not to be working with open source modeset driver (radeon)?

Anyway you have to install xorg-drv-video-fglrx, then check that driver is installed and compiled correctly with sudo dkms status, then remove /etc/X11/Xorg.conf and reboot (of course this should be done after installing the system or using livecd on a persistent pendrive).

Actually I have 3 Linux distros in this laptop! Debian, Fedora & Ubuntu...

In all 3 I had to download n install Fglrx drivers, as open source "mesa' drivers (if i am not mistaken it is called) was overheating my laptop!