Exec    "I"     exec xmodmap -e "pointer = 1 2 3"

in your .steprc file in the Function Definition Section under "Init Function"

Otherwise, put

        xmodmap -e "pointer = 1 2 3"

in a file sourced after X starts up
(don't ignore the spaces between the numbers).

You can experiment with the number order to customise the mouse to your liking
(1 being the left mouse button, 2 middle, 3 right).

For a Kensington Thinking Mouse, I would suggest "pointer = 1 3 2"
as the buttons have a different configuration from most 3-button mice.

http://www.mit.edu/~locutus
locutus@mit.edu

Jon Howell has hacked together a patch which uses three-button
info available from mice that support (I think) the extended mouse
protocol (handler 4). It currently requires you build your own
kernel, since it's not in its finished form yet.
 
Get:
  ftp://ftp.cs.dartmouth.edu/pub/jonh/mouse-hack.0.2.tgz 
It comes with a README.
 
If you don't have kernel source and want to save a little time, you can
use a prebuilt 2.1.14 kernel:
  ftp://ftp.cs.dartmouth.edu/pub/jonh/vmlinux.2.1.14.mouse-hack.gz 
 
jonh@cs.dartmouth.edu
 
Please make an entry here if it works or doesn't on your brand of
mouse, to save others the time messing with it:
 
mouse                               status   reporter
Logitech corded MouseMan            works            jonh@cs.dartmouth.edu
Kensington Thinking Mouse           works            sharding@oregon.uoregon.edu
Kensington Thinking Mouse           works!           bjorn@daimi.aau.dk
     I followed the instructions in the README exactly and used
     kernel sources from 970218.
Kensington Turbo Mouse 4.0          doesn't work     phiber@radicalmedia.com
MouseSystems MacPoint Pro           doesn't work     wsears@stsci.edu
     However, if you use 'mousemode 2'  you can use MacX mode like 
     the MkLinux people. (I am using the 2.1.24 #419 Thu Mar 13 11:39:34
     kernel, not the precompiled one above.)
MicroSpeed Mouse Deluxe MD-310      doesn't work     daniel@ap-kas.ie.philips.com
     Kernel 2.1.24 of 970422 and mouse-hack 0.3
     Output of scanmodes.pl: "Your mouse supports these modes: -1 1 47"

Note: If your mouse doesn't handle extended ADB mouse protocol, it
probably works as a MacX mouse. This means that the second and third
buttons show up as the left and right arrow keys. (All MouseSystems
multi-button mice, for example, are in MacX mode all the time, and
respond improperly to commands to change handler #, but their MacOS
software looks at the arrow keys to see which device they come from.)

The simple way to use a MacX mouse in X is to set the -middlekey and
-rightkey to the keys your mouse is sending (I think 56 and 57 are the
left and right arrows? Try an xmodmap -pke under X to confirm this).
Your mouse buttons may still require you to hold the option key down
to be used. If so, you can set -nooptionmouse, but be aware that your
left and right arrows will not act like your mouse buttons--you'll have
to hold down the option key to use them as keys.

--andi payn, payn@null.net