Linux.com: Mapping Extras Function Keys with XFree 4.0Feb 23, 2001, 20:34 (2 Talkback[s])
(Other stories by Josh Boudreau)
"This article will explain the process of getting your keyboard's extra function keys to work in XFree86 4.0.X. This article uses the Logitech iTouch keyboard with XFree86 4.0.2 as an example. This method has not been tested with other keyboard models and XFree86 versions other than the ones used by myself. Your results may vary depending if your keyboard is supported by XFree86 4.0 or not. As far as I know, this is an undocumented feature that has been incorporated in XFree86 4.0."
"The way this works is that you have to get the scancode of your extra function keys with the xev program, and assign names and keysyms to the keys to be able to use them with X11. I suggest you backup the files we are going to edit in case something goes wrong and you need to restore the original configuration."