You are correct that the 990 would certainly not work with a USB wireless adapter. The airport express, though, is technically a wireless bridge or router depending upon configuration (acts as a print server), which makes it a master unit and not a slave. By this token, with the appropriate coding I assumed that such communication with the 990 would be possible, but that is purely speculation on my part.

My earlier post does read like the express' USB port is viable for upgrades, though, don't it? I was thinking of using the USB connection in terms of directly to my PowerBook (laptop), which of course I can connect temporarily as needed. Those with G5s won't have that luxury. Thanks for noting the error on my part.