Performance problems after o.s. upgrade

[fra83fra]

Hi all, I have a GeForce 7600GS on Athlon 3000+ PC.
in this days i upgraded my o.s. to Mandriva 2008 32 bit.
In Mandriva 2007 64 bit I had before, games such as Tremulous or Doom III run with very high fps (e.g. trem at 125 fps auto-limited), with previous nvidia drivers (I think 96.xxx or similar), with or without beryl - no difference.
Now I have newest 100.xx drivers, installed automatically via mandriva repository (the official installed had problems compiling kernel module). I copied the old xorg.conf.

The problem: now I have very low fps, in tremulous it is 25 or less when in action and it's unplayable. Compiz is not installed. I tryed to change everything in xorg.conf, I changed the AGPGART module I used in old system to use the nvidia_agp, I have everything "ON" (Fast writes, SBA, direct rendering, ...) etc. but it's so slooow

Please help me how can I have the performace I had with previous system? should I reinstall old nvidia drivers?

Many thanks in advance