To remap the zoom, favorites, shortcut buttons, etc. on a Microsoft Natural Ergonomic Keyboard 4000, when using Apple OSX, the USB Overdrive utility works very well. Just open the preferences pane, and hit the special key you want to modify. It appears in the list, and you can remap it to anything.
For a more complex solution, which is powerful but harder to pick up, try [ControllerMate][http://www.orderedbytes.com/controllermate/].