'showkey -s' (console) and 'xev' (X11) could help you finding the key codes. I haven't worked with .Xmodmap yet, but I have a fealing it will overwrite the global /etc/X11/* settings
edit: it seams that I've found something. (but I can't test it until I'm sitting behind my own computer)
- list of keyboard models. find your model here!
- configuration of the keyboard symbols. (if you want to check your re-model)
- index of the keyboard symbols.
my personal conclusion: edit /etc/X11/XF86Config (or /etc/X11/XF86Config-4), and change the "XkbModel" in your keyboard model to make the special keys work
in my case: "XkbModel" "compaqeak8"
..to reconize the compaq-easy-access keys.
the special keys didn't work again after I'd upgraded my system