scroll wheel

i'm trying to get the scroll wheel on my micro$oft intellimouse optical (usb) to work. the mouse itself works great, but i can't get the scroll wheel to work, even though it seemed to work fine when i installed linux on my system (mandrake's install requires that you move the scroll wheel in order to calibrate and setup the mouse).

any idea where i should start in order to get this working? i've tried using gpm... maybe i'm just not doing something right, i dunno... but i can never get it to work.