How to create shortcut to turn on/off Wifi in Snow Leopard

I want to use the F5 key on my MBP to turn on Wifi with a single hit on the keyboard and turn it off again with a single hit using F6. Is this possible? I've tried to do it under Preferences/Keyboard/Keyboard Shortcuts but I can't add F5 (not by typing and not by hitting that button). That button seems to be dedicated for the illumination of the keyboard. How can I change these settings so that I can have my fast function key at my disposal.

Cheers,

BassPlaya