Well, when I use the WaveLAN card in my iMac G3, PowerBook G3, iBook, and Power Mac G4, OS 9 drivers detect it as true-blue AirPort. I seem to remember OS X had some issues, but I haven't tried it on an OS X machine recently. (The AirPort card essentially *IS* an AirPort card; as bunsen mentioned, the original "UFO" AirPort base stations actually contain a WaveLAN card inside! That's where one of my WaveLAN cards came from.)

I don't know about Extreme-compatible ones. I wasn't even aware that there were Extreme-driver-compatible PCMCIA (not mini-PCI) cards. The sticking point I can see is that the AirPort slot is not a CardBus slot, but just a plain old fashioned PCMCIA slot; and I would imagine that all Extreme-compatible cards are CardBus. (PCMCIA is based on the old ISA standard, CardBus allows the same pins to transmit PCI instead of ISA, for CardBus cards. While the CardBus slot is backward-compatible, so the slot detects which type of card you have and sets itself to the proper mode; CardBus cards tend not to be backward compatible, only using the newer PCI interface.)