AirPort Extreme cards are not even vaguely similar to the older AirPort cards. Older cards are similar to a PCMCIA card, using the same form factor and connector. Extreme cards are mini-PCI cards, very much intended to be internally installed rather than popped in or out.
You CAN use a commercially available PCMCIA wireless card in an available PCMCIA slot, as long as the manufacturer provides Mac drivers. You can also use a USB wireless adapter, again assuming it comes with proper drivers.