I am using a M$ optical USB IntelliMouse and cannot swap the 1st and 3rd buttons via the left-handed button mapping option in the KDE configuration environment (the left-handed option is there, but is not clickable). It works with
# xmodmap -e "pointer = 3 2 1 6 7 4 5"
but the change only applies to the current X session.
While googling for a solution, I got the impression that a script could be written -- .Xmodmap in the home directory -- that runs the above code each time X starts (writing such a thing would surely consummate this new and joyous partnership Linux and I are developing ).
If someone knows of a way to sinisterize my mouse more permanently than the above, please post.