Actually, I'm starting to suspect that the switch is bad. I connected my XBOX via the same switch and it gave very unreliable results - packets from the internet were just going missing on the return path.
So I could see tracert/ping info leave the switch and return to the switch but not to the correct port.
In case anyone happens to buy one, it's a Corega 5 port switch and cost about £30.
It's in the bin now, replaced with a £30 netgear hub, and all is happy, Rio and XBOX working great.
Paul.
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Paul Haigh, Reg. 4120
(mk1) 6GB, Blue, 00254
(mk2) 12GB, Red, 00357