I recently decided to try running Beryl (an offshoot of AiGLX which is an offshoot of XGL) and found 2 good guides thanks to some quick searches on the Ubuntu forums.
The Radeon Driver howto is excellent and works very well with the older Radeon 9000m card in my laptop. This got the Direct Rendering working using the open source ATI drivers.
The Edgy AiGLX - Beryl guide finished it up nicely leaving me with a simple desktop with lots of funky effect to serve no purpose other then to look good. 
I would not suggest running OpenGL games while running AiGLX since there is still major performance problems as the AiGLX uses up most of the Direct Rendering leaving little left for games. So if you are not running any games it’s a great desktop and if you do decide to fire up Quake4, UT2003 or Postal 2 be sure to log off and log on with another session that doesn’t use the AiGLX
Recently Commented