look at xrandr !!!

Drivers:

xserver-xorg-video-ati
xserver-xorg-video-radeon

http://wiki.x.org/wiki/radeon/
https://packages.debian.org/search?keywords=xserver-xorg-video-radeon
http://packages.ubuntu.com/search?keywords=xserver-xorg-video-radeon
https://packages.debian.org/sid/xserver-xorg-video-radeon
https://wiki.debian.org/AtiHowTo