Ok, so it has ended up as a one person conversation. I have found the problem - as described already in another thread on using the interrupts. Basically it would appear the documentation on using it is lacking some of the details (perhaps many already know enough that this seems obviuse). Anyway, the answers are here:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1172808516/1
Could we have a contributor to the wiki update the docs to at least point here? It could save many others much more time.
Thanks,
Josh