# ~/.xinitrc
xmodmap -e "pointer = 1 2 3 8 9 4 5 6 7 10 11 12 13"
imwheel -f -k -b "67"

# ~/.imwheelrc

".*"
None, Up, Alt_L|Left
None, Down, Alt_L|Right

# /etc/X11/xorg.conf

Section "InputDevice"
        Identifier      "Mouse0"
        Driver          "mouse"
        Option          "Protocol"              "ExplorerPS/2"
        Option          "Device"                "/dev/input/mice"
        Option          "Buttons"               "9"
        Option          "Emulate3Buttons"       "0"
        Option          "ZAxisMapping"          "6 7"
EndSection

***SOS-REFERENCE*** ---> http://gentoo-wiki.com/HOWTO_Mouse_Nav_Buttons