I'm just going by teh product page.
There's an Orinoco PCMCIA card that has drivers that go all the way back to 7.5, though. If you have something old enough that it has a PCMCIA slot you can definitely find other cards.
Toilet seat iBooks were the first to have the Airport slot, and then the first Powerbook was the one that came out the following winter/spring (Pismo), which is easily identified by its Firewire port. Basically it works like - if your Mac notebook has Firewire, it has a slot for an Airport card.
Some folks might not want to spend the ridiculous price that an Airport card commands nowadays though - last I looked (whcih has been a while) they were selling on eBay for upwards of $70. IF the machine isn't used on your lap a whole lot (always ona desk) then USB would be reasonable.
I do not understand what I do. For what I want to do, I do not do. But what I hate, I do.