xorg.conf:
Section "InputDevice"
        Identifier  "Mouse0"
        Driver      "mouse"
        Option      "Protocol" "ExplorerPS/2"
        Option      "Device" "/dev/input/mouse0"
        Option      "ZAxisMapping" "6 7 4 5"
EndSection


.xinitrc/.xsession:
xmodmap -e "pointer = 1 2 3 8 9 4 5 6 7 10 11" &
fluxbox