Since I own a PB "Lombard" (bronze), I can't use an Airport card from Apple. "Thanks Apple." Apple suggested I buy a newer PowerBook, or they recommended a WaveLan card from Asante costing $129 and which may not work with OSX.
Short of either of those options, I found drivers that support PRISM & PRISM II chipset PC cards, and then I bought a $42 PC wireless card from Linksys. OSX drivers for the Linksys PC-card are found at Rob McKeever's mac.com page.
So far everthing works great, minus WEP. Best of all, it is free. NOTE: These drivers break in Jaguar and will probably require an update to function again.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020820010705364