Hello, I thought it best to let you know that I setup a new less complex scenario and the network rendering is functioning very happily!  That's from a Vista 64 bit machine to two XP 32 bit OS machines, one with 2 cores and the i7 with 4.

I guess my first scene was just too much for them to cope with...

Thanks for your advice while I wrestled with this one.  When the event I'm doing this for is over I'll post a link ;)