Will a third-party wireless network PCMCIA (PC) card for my Macintosh PowerBook work in the AirPort slot inside a wireless capable Macintosh such as the iMac (Slot Loading), Power Mac G4 (AGP Graphics) or PowerBook (FireWire)? What about the opposite?

No. There is an Apple AirPort Card designed specifically for Macintosh computers that support the AirPort wireless networking system. Refer to the printed materials that came with your computer to determine if it will support AirPort.

Conversely, you cannot use the Apple AirPort Card in the external PowerBook PCMCIA card slot.