Microsoft USB Optical IMPS/2

I just got a usb optical intellimouse.
I'm assuming I continue to use the IMPS/2 like I have been with my
current standard intellimouse.

But I can't seem to get the roller wheel working. I have the
Option "ZAxisMapping" "4 5"

set correctly.. If I put my regular intellipoint mouse on it everything
is peachy, but when I switch and restart x the wheel just won't spin!!!

Any ideas? faulty mouse?

Thanks.