Forwarding this bug from Ubuntu:
https://bugs.edge.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/353996

[Problem]
Poor performance with Xorg process CPU load between 20%-99%.  Resolved after setting AGPMode 4 (and a few other things... see xorg.conf).

[Original Report]
Binary package hint: xorg

Hi, well this is my second time, trying to migrate to Jaunty 9.04. But still having the same problem, the IBM Thinkpad T40 - Video ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500] is not working properly, in fact it's very slow, and use the Xorg process between 20% to 99% of my CPU.

In Intrepid 8.10 it works perfectly, now I will attach some files than may be can help.

Please let me know how can I help to fix it.

<later>
Well. Finally I found the way to make works it.

I did change the /etc/X11/xorg.conf file, Now it's working fine

Let me show you: with this configuration the system is working like with Intrepid.

Section "Device"
 Identifier "Configured Video Device"
 Boardname "ATI Radeon"
 Busid "PCI:1:0:0"
 Driver "radeon"
 Screen 0
 Vendorname "ATI"
 Option "MergedFB" "off"
 Option "AccelMethod" "EXA"
 Option "EXANoComposite" "false"
 Option "FBTexPercent" "50"
 Option "MigrationHeuristic" "greedy"
 Option "DRI" "true"
 Option "GARTSize" "256"
 Option "AGPMode" "4"
 Option "Colortiling" "On"
EndSection

Section "DRI"
 Mode 0666
EndSection

Section "ServerLayout"
 Identifier "Default Layout"
 screen 0 "Default Screen" 0 0
 Option "AIGLX" "true"
EndSection

Section "Extensions"
 Option "Composite" "Enable"
EndSection

Section "Monitor"
 Identifier "Configured Monitor"
EndSection

Section "Screen"
 Identifier "Default Screen"
 Monitor "Configured Monitor"
 Device "Configured Video Device"
EndSection

----
00:00.0 Host bridge: Intel Corporation 82855PM Processor to I/O Controller (rev 03)
00:01.0 PCI bridge: Intel Corporation 82855PM Processor to AGP Controller (rev 03)
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500]