Lo correcto :
http://www.xfree86.org/current/mouse5.html
Lo incorrecto : mi xorg.conf -P en slack 10.2
Section "InputDevice"
# Identifier and driver
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/mouse"
Option "ZAxisMapping" "4 5"