On newer PowerBooks that don't allow booting into OS 9 (where you could gain full acces to all function keys), there is a utility called fnSwitch that will do this under OS X. It is stable under 10.2, but crashes under 10.3. I understand that fnSwitch will be updated for 10.3.
However, I bravely installed it under Panther, and although it crashed, it still returned access to function keys! Now I can use function keys for my Quickeys shortcuts!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031101124224608