the oss should support it according to the official blog
(see: http://tirdc.livejournal.com/ )
the fglrx supports it too, including aiglx from the 8.42.3 release.
in older releases for compiz/beryl you would have had to use xgl.
to enable rendering in xorg use:
in yourOption "RenderAccel" "true"andSectionDevice
this things have been covered a lot in the 8.42 thread in this forum and get out if you take the time to make a search on this forum.Section "Extensions"
Option "DAMAGE" "true"
Option "RENDER" "true"
Option "Composite" "Enable"
from the last 2 releases of the fglrx (8.41.7 and 8.42.3) the performance of the ati boards aren't too far away from windows and from nvidia boards. for a comparison see this article:
where the fglrx 8.42.3 with a hd2900 performs about 20% better than the driver in windows vista.