I have a problem using airtunes and printing through the Airport Express, and I have tried everything I know.

My set-up is as follows:
-internet (not a fixed IP) comes in to Origo ASR-8400 router
-router is connected by ethernet cable to Airport Express (in bridge mode)
-Canon MP160 printer is attached to Airport
-speakers are attached to Airport

I have two Macs: a MacBook and a Powerbook G4. The Macbook has an airport card and can connect to the Airport Express, print and play music without problems.

The G4 has no airport card anymore, but connects wireless to the internet with a USB dongle (Zydas SWMULZ-5400). The internet works fine that way - it picks up the Aiport Express signal. However, the G4 will not recognize the Airport Express in Airport Utility and it will not print or play music wireless. If I connect the G4 directly to the Airport Express with an ethernet cable, all works fine. Same if I connect the G4 to the router with an ethernet cable (and the router is connected to the Airport Express); it also all works fine.

I tried putting the router in half bridge mode, in full bridge mode, but nothing seems to make a difference. I have a .Mac account, so Back to my Mac should work, but it is iffy (and only works if I have the router in half-bridge or bridge). The two computers do connect to each other though (connect to server) so I also can play music or print from the G4 via the Macbook (so the G4 connects wireless to Macbook, which will make the connection to the Airport Express). BUT WHY doesn't the G4 recognize the Airport Express??

Does it have to do with AppleTalk? With Bonjour? My set-up? I just don't get it. Help is much appreciated.