I saw this today on the Ubuntu forums and thought it might help people using older ATI graphics cards running KDE 4.2. This is taken directly from the post.
radeon driver improvements
KDE 4.x replaces the infamous kicker panel with plasma. Plasma makes heavy use of argb, which hammered my ati card. It's an old card and the proprietary drivers don't support it. The new radeonhd drivers don't support it.
I'm using a FireGL 9000 (chipset r250).
Using the autogenerated settings, my CPU was running at anywhere from 30 - 80 percent load, just to support the desktop. Needless to say, actually using the computer was a real challenge.
After doing some looking around on the net and experimenting with some different values, I have come up with an xorg.conf file that lets me use the radeon driver for KDE 4.2 without stressing the hell out of my CPU.
Identifier "Configured Video Device"
Option "AccelMethod" "EXA"
Option "MigrationHeuristic" "greedy"
Option "AccelDFS" "true"
Option "EnablePageFlip" "true"
Option "EnableDepthMoves" "true"
Option "AGPMode" "8"
Option "ColorTiling" "on"
Identifier "Configured Monitor"
Identifier "Default Screen"
Monitor "Configured Monitor"
Device "Configured Video Device"
My CPU is now running 1 - 5 percent, to support the KDE desktop. Needless to say, I am pleased. I do not claim that this is perfect and I would certainly appreciate any feedback / advice on what I've come up with. When jaunty hits gold, it would be nice if we could have some documentation to help people use older ati cards with modern desktops.
This guy had success, hope his experience will help others.