Whilst looking for something else, (Yet another new router), I found the answer to an earlier question of mine, i.e. What 'other application' had changed my network settings? Apparently the router itself had done so.
See http://en.allexperts.com/q/Macintosh-OS-1063/2008/11/t-Access-Network-System.ht
And v. interesting it is too.
Eric Jervis 