It is indeed *really* hard to get the airport card out of those last model powerbooks, or at least I remember it being so. (It's been a few years, but I recall thinking you might have to pull the motherboard to get it out.)

Drivers undoubtedly will be an issue but it's an interesting thought. A great source for mini-PCI cards to play with is old wifi routers; I've retrofitted several x86 laptops with very nice (linux friendly) Atheros cards out of SMB-grade Netgears. That said, the best I've seen so far are 802.11a. (wonder if I have any left, come to think about it.)