ok, it worked briefly (then the machine couldn’t find the itunes server again, but that’s another problem!)
I don’t precisely know what kicked it into action, but it suddenly started working after doing the vista registry hack needed to allow you to get access to network shares under vista on a readnas box( http://kbserver.netgear.com/kb_web_files/N101700.asp#Why_am_I_not_able_to_access_ReadyNAS_share_that_is_password_protected_with_Vista.3F )
I’m pretty sure this was what got it working (but not 100% sure!)