backup your /etc/X11/xorg.conf file then open ut up and look for the mouse section in "input devices" look for a line that says somthing like....
Code:
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "IMPS/2"
for whell mice i think the driver has to be IMPS/2. if it isnt, change the driver.
then under the driver line, add these 2 lines
Code:
Option "ZAxisMapping" "4 5"
then logout, and restart the X server b hitting ctrl+alt+<backspace>
does it work now ?
if not, replace the config file with the backup, and no harm is done.