I thought I'd share this after several hours of frustration setting up an Airport express with a WEP encrypted network. I thought I had fully disabled all password protections on my network, but apparently it was still protected. It would detect the airport, allow me to reconfigure it, but then the airport would not restart properly. Finally, I switched from WEP 128 to WEP 40 and voila, problem solved. The modem/router had been on WEP 128, but only picked up the airport on 40 (and I don't even know what these things mean!) Anyway, maybe there is someone else out there who is about to throw their airport express through their wall for the same reason. Perhaps this will do the trick.