This was it. Plugged both the server and the Rio into a 10mb hub and they talked. Worked beautifully. Since the switch is not managable, I guess I will need to put a hub in between the Rio(s) and the switch. (With Rio's running $149 at Fry's, I should pick up a couple more :-)

But what's up with the autosensing? My switch has worked fine with all my other devices (as I moved them from 10 to 100) but the Rio had a problem with it... oh well, it works now.

Vince and Tony, thanks very much for your help.