I tried again to set NvAGP to 1.
The same thing happend, but when I looked in the var/log /warn there was nothing wrong to see.
For a while I couldn't start some games at all, like Tuxracer. I changed the mouse and the keeboard and now I am able to start it, but in some slops like "who says pinguins can't fly" sometimes the whole screen begins to shake and after some second freezes. This happens both when I don't set NvAGP and when I do set it to 0,1,2, or 3. When I don't set it I get the warning about "insmod agpgart", but when I set it the problems persist without the warning