Hi, pmorr. If you want an Apple wireless card, then yes, it will have to be the original Airport rather than an Airport Extreme card (the Extreme card doesn't fit into a Tibook, physically). But original Airport cards are extravagantly expensive now, and there's no compelling reason to buy one. There are several good third-party wireless cards that will go into your Powerbook's PC card (CardBus) slot and provide performance equal to or better than an Airport Extreme Card (same speed, greater range) provides in AE-equipped Aluminum Powerbooks. They use Apple's own drivers, so they require no third-party software, and they set up just like Apple's cards. The only downside to using one is that it ties your CardBus slot up. Here are three such cards:
Sonnet
MacWireless
Buffalo