When commenting on this on TAB's site with regard to the new AirPort software, someone made a suggestion that solved all my problems: Use WPA/WPA2 instead of WEP security. Well, I was using WEP. I switched and ... now it works! At least the Express can now join my Extreme network, and I can play iTunes music through the speakers. I haven't been able to set up a WDS network yet, but at least basic functions are possible now. Give this a try if you are having similar problems, and someone at Apple needs to make this part of their support suggestions.

