Ok here an update
I tested the 8.7 8.8 8.9 driver on two machine one with a hd3780 and hd 2600 pro AGP
Both system are running Mandriva Linux 2008.1
with the 8.7 driver compiz work great but the log out bug is present (X crash)
with 8.8 and 8.9 no compiz KDE 4.1 is also extremely slow
In all case 3D acceleration work fine without Compiz.
So what change in the 8.8 and 8.9 driver that could cause this issue.
PS: xorg.conf is exactly the same whit all those version