Try these links.
http://www.amazon.com/s/?ie=UTF8&keywords=g4+airport+card&tag=googhydr-20&index= aps&hvadid=25180097311&hvpos=1s1&hvexid=&hvnetw=g&hvrand=830038757339670469&hvpo ne=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_66z07os7mf_b
Hello and welcome to the support community
We need more details on what is wrong with your powerbook. For example you can't connect to a wireless network as you get an error or the airport doesn't show active. The problem may not be with your airport card but any number of things like software or the antenna.
If you want to trouble shoot the issue here are some links to tips.