Edit the pointer section of /etc/X11/XF86Config-4 to look like this,
Code:
Identifier "Mouse1"
Driver "mouse"
Option "Protocol" "ExplorerPS/2"
Option "Device" "/dev/psaux"
Option "Buttons" "7"
Option "ZAxisMapping" "6 7"
Keep what ever device you have there already if it working now.
To get the wheel working properly you need to do the xmodmap part in a terminal whenever you startx or add it to a script that runs when you boot/startx.