Comment 3 for bug 509632

$ dpkg -l kdebase-bin xserver-xorg xserver-xorg-core xserver-xorg-video-i128 && uname -mr
Desiderato=Unknown/Install/Remove/Purge/Hold
| Stato=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/ Err?=(nessuno)/Reinst-required (Stato,Err: maiuscolo=grave)
||/ Nome Versione Descrizione
+++-==============-==============-============================================
ii kdebase-bin 4:4.3.2-0ubunt core binaries for the KDE 4 base module
ii xserver-xorg 1:7.4+3ubuntu1 the X.Org X server
ii xserver-xorg-c 2:1.6.4-2ubunt Xorg X server - core server
ii xserver-xorg-v 1:1.3.2-1 X.Org X server -- i128 display driver
2.6.31-17-generic i686

glxinfo has a long output, if you want I will attach it here.
I will try all your suggestions as soon as possible.
By the way, I have enhanced Ubuntu's desktop effects enabled. I will also try to disable them.