My vagaries:

• I have successfully used an "AirPort" card in a regular PCMCIA slot, and it is recognized as a Lucent WaveLAN Gold card.
  
• I have successfully used a Lucent WaveLAN Silver card (itself pulled from an original Apple AirPort Base Station,) in an AirPort slot.
  
• This weekend, I will try a PCMCIA flash memory card (same physical size as an AirPort card,) in an AirPort slot to see what happens.

Technical notes:

• The original AirPort card is an 802.11b-only card in the form factor of a 16-bit PCMCIA card.
  
• The original AirPort card slot is a (supposedly slightly modified) 16-bit PCMCIA slot. It is not a 32-bit CardBus slot. Therefore newer CardBus 802.11g cards will not work in it.
  
• The original AirPort Extreme card is an 802.11b/g card in the form factor of a standard 32-bit mini-PCI card.
  
• Later (802.11n) AirPort Extreme cards are mini-PCI-Express cards.
  
• Any 802.11 card that uses the same basic interface and chipset as its equivalent official Apple card will be identified by the OS as if it WERE an official Apple card. Hence the reason the CardBus 802.11g card is recognized as an AirPort Extreme card - it uses a 32-bit PCI connection (over CardBus instead of mini-PCI) and the same chipset as the AirPort Extreme, so the OS doesn't know the difference. Likewise a WaveLAN card identifies as an original AirPort card (because they are in fact the same physical card inside.)

It *MAY* be possible to use a 16-bit PCMCIA 802.11g card in the original AirPort slot, but I have only ever been able to find *ONE* such card, and I haven't bought one to test it out.