From Compiz

There are two drivers for ATI cards: fglrx and the free drivers.

Fglrx

Fglrx is the official ATI's driver. Latest version works only for Radeon 9200 and newer versions. Older versions of fglrx (up to 8.28) work with older cards too. It is recommended, if you have any card up to 9200, to use the free drivers, otherwise use fglrx. Fglrx doesn't support AIGLX. That means you must use XGL with it. AIGLX support is expected to be added in next few versions (few months). Get fglrx here.

The free drivers

There are two types of free drivers: r200 and r300. r200 is used for Radeons up to 9200 and r300 is used for Radeons 9550 and newer. r200 is stable, but r300 is experimental. If r300 is too unstable for you, try fglrx driver. Both r200 and r300 support AIGLX. To install them, get Mesa and xf86-video-ati package.

In Ubuntu, this driver is installed by default. You can either set it through running a "dpkg-reconfigure xserver-xorg" as root, or by manually editing '/etc/X11/xorg.conf'.

Below are some common Options that can be added to the Device section for increased performance:

Option		"DRI"			"true"
Option		"ColorTiling"		"on"
Option		"EnablePageFlip"	"true"
Option		"AccelMethod" 		"EXA"
Option		"XAANoOffscreenPixmaps"
Option		"RenderAccel"		"true"
Option 		"AGPMode" 		"x"
Option		"AGPFastWrite"		"on"

You can fiddle with these options to find the best combination for you. The following combination is one confirmed to work on most Radeon cards with good performance:

Option		"DRI"			"true"
Option		"ColorTiling"		"on"
Option		"EnablePageFlip"	"true"
Option		"AccelMethod" 		"EXA"
Option		"XAANoOffscreenPixmaps"