Microsoft Trackball Optical 5 button function

[mbmumme]

I have a Trackball optical USB with 5 buttons. The 2 main buttons are functional and the wheel works fine. I am looking the solution on mapping the outside buttons and the wheel button. Mainly the outside left I want mapped to be a back button in my browser. I accomplished this in Ubuntu but can't seem to get it to work in Sabayon. I know it involves imwheel but for the life of me I can't remember how to obtain or install. Any tips would be appreciated including setup scripts for xorg. Thanks in advance!!