Yeeaahh !!
I resolved my problem !
It seems that AGPART bugged...
I put in my XFConfig-4:
Option "NvAgp" "1"
$ glxgears
10064 frames in 5.0 seconds = 2012.800 FPS
11140 frames in 5.0 seconds = 2228.000 FPS
Finally I am with kernel 2.6.0, Debian GNU/Linux sid, and package XFree experimental 4.3, and NVIDIA drivers 5328.