Ok, I got it working. This works with my Intellimouse 3.0 and should work with any 5 button mouse. The only thing you might have to toy around with is the xmodmap button order in combination with the number of buttons.
First thing was to change the xorg.conf file. I'm not sure if every single statement is necissary, but this worked for me. Too much is better than too little.
Code:
Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "CorePointer"
Option "Protocol" "ExplorerPS/2"
Option "Device" "/dev/input/mice"
Option "Buttons" "7"
Option "ZAxisMapping" "6 7"
EndSection
Next was to insert the xmodmap statement into a file called mouse.sh. Create the mouse.sh file under /etc/X11/xinit/xinitrc.d/ and give it execute rights. The file should contain the following statements.
Code:
#!/bin/sh
# /etc/X11/xinit/xinitrc.d/mouse.sh
# Required for the configuration of a 5-button mouse
xmodmap -e "pointer = 1 2 3 8 9 4 5 6 7 10 11"
Again, i'm pretty sure the first part is just interpreted as comments. Not entirely sure if they are needed at all.
The xmodmap statement is what most people will find themselves messing with the get the proper functionality of each button. This setup should work for anyone with an Intellimouse 3.0. mouse.sh is run on startup via xinit so the session does not need an extra script or command under startup programs for it to work.