I've got the same probleme...
Leadtech Geforce 2mx
and ~600 fps in glxgears.
but, as I never play, it's not a probleme for me
now, have a look in this threads :
plz note, on the end of the thread :
I found What what wrong!!
Is a kernel issue!!
I boot with the paramater
and now my FPS are at ~3000!!!!!!!!!!!!
before they where ~500
but .. if I boot with that kernel parameter I DONT HAVE SOUND...... AND NO WIRELESS INTERNET CARD....
so is a question ... of SOUND or VIDEO
I just compiled the kernel 2.5.64!!!!
and all my stuf work!!!
sound! alsa! great
wireless is working great!!!
IM SO HAPPY!!
it was a kernel problem!!
hope it will help ...