try adding this line to your
mouse config in the XOrg's config file you mentioned above:
Option "ZAxisMapping" "4 5"
so after you've done that, the section looks like this (I copied the other lines from your post):
Section "InputDevice"
Identifier "Mouse0"
Driver "
mouse"
Option "Protocol" "auto"
Option "Device" "/dev/mouse"
Option "ZAxisMapping" "4 5"
EndSection
that should do the trick. restart your X and see..
EDIT: SBing, seems like you were quicker and did the job while I was only writing..