You can put a standard AirPort card in the Dual 867. This card will then work with any AirPort or AirPort Extreme base station. But don't forget, the original AirPort max speed is 11Mb (as opposed to the AirPort Extreme max speed of 54Mb).
Apple has not delivered an AirPort Extreme card in the original AirPort card enclosure. I wouldn't be surprised if someone has released a PCI card capable of AirPort Extreme speeds.
Tim