strim, that is why you have to use stuff with broadcom chipsets with airport extreme drivers, and if he has a USB pccard, stuff with ralink chipsets that have drivers for OS X.(very very shitty ones, but they .. sometimes.. do not totally screw your network and cause kernel panics... sometimes.

I bet there are USB broadcom based things that may work as well, but I do not have facts to back that specific situation up.

Seriously, in 10.3 with up to date airport software you are laughing with an airport extreme compatible card.