I'm currently using my Microsoft IntelliMouse Explorer 3.0 USB on my iMac Intel(1st ed).. By default when I hooked it up it assigned all the buttons except the top side button a function; the lower side button -> expose, scroll wheel button -> dashboard, left mouse button primary, right mouse button secondary..

I want to get it so that when I click the top side button it would shortcut to the desktop, which I believe is F11 on the keyboard(default). When I went into System Pref. -> Keyboard and Mouse, I did not see any option for assigning shortcuts to buttons other then the keyboard.