I feel so stupid. After hours of research and faffing about I went to play with the RaspPi, trying to use SSH or VNC. This tied up the USB lead I was using.
"I'll have one last try", I thought, and grabbed the cable for my Kindle. Up popped the message about an unrecognised keyboard being connected. Off to load Arduino IDE (1.0.5) and everything is working.
Moral of the story - check the cable!