kubuntu and graphic acceleration

[Luca Ferrari]

Hi all,
I'm running kubuntu 9.1 on my acer aspire 6935, and justa  couple of minutes 
after the desktop has loaded a message alerts me that graphic composition has 
been disabled because it was going too slow. The dock becomes gray and no 3d 
effects are enabled. Now, since it has worked fine on previous version of 
Kubuntu, anybody has experiencing the same problem and/or have any suggestion?


Thanks,
Luca