You could attempt to use Yast, though in my experience it doesn't always do such a good job with the correct detection of mice.
I'd open up your X config file (/etc/X11/XF86Config-4) as root, back it up, then find your mouse entry and add a line for Z Axis mapping, e.g.
Code:
Section "InputDevice"
Identifier "USB Mouse"
Driver "mouse"
Option "Device" "/dev/input/mice"
Option "SendCoreEvents" "true"
Option "Protocol" "IMPS/2"
Option "ZAxisMapping" "4 5"
Option "Buttons" "5"
The other options may vary, depending on where your mouse is connected etc.
Good luck
mj