Locate this entry in your /etc/X11/XF86Config file:
Code:
Section "InputDevice"
# Identifier and driver
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping""4 5"
# Option "CursorShadow" "on"
# Option "CursorShadowAlpha" "40"
# Option "CursorShadowXOffset" "4"
# Option "CursorShadowYOffset" "2"
# When using XQUEUE, comment out the above two lines, and uncomment
# the following line.
Notice the Option "ZAxisMapping" "4 5"
That's the one you want
Cool