How do I use a USB wireless adapters w/ PowerBook


Ok, here is my situation:
I have a Windows desktop hooked in to my wireless router (Trendnet TEW-431BRP) and I also have 2 laptops: a) a Windows based one which I have just connected via a USB wireless adapter and b) a 12" Powerbook (867Mhz) which I would like to connect using the same USB adapter (since I can't use 2 laptops at once).

However, when I plug the USD wireless adapter into the PowerBook and go to "System Preferences-Network" all I can find is connection via:
Built in Ethernet
Airport Express (which I do not own)
Internal modem.

How do I get it to recognize my USB port as a wireless connection?

Or, do I need to get an adapter (USB to Ethernet) and plug it in that way instead?