All three were on the same powered USB3 hub. I've moved the Duemilanove to a separate USB port on the front of the computer and now they don't interfere with each other. So, now the question is why does this happen on the powered hub?
Thanks very much
[edit] Actually there is still some interaction. Starting up the IDE on one port still resets the other but unplugging one doesn't reboot the other.
Pete