Normally this is resolved by simply editing your /etc/X11/XF86Config file. Here's an exerpt from mine, you may have to tinker around with some of the options for yours to work (this is from the Pointer Section or Mouse Section):
Code:
Section "InputDevice"
# Identifier and driver
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "IMPS/2"
Option "Device" "/dev/input/mice"
Option "ZAxisMapping""4 5"
The main part of that to note is the ZAxisMapping. That line is the scroll line
Cool