Thanks for the confirmation Daniel.
Not sure about the OP but yes for my situation, the users are created on the main site from AD and managed from there through a single sign on process. All I am then looking to achieve (later in the summer) is allowing users, who have already signed on to the main Moodle site, to be able to click a link through to the separate archive site(s) without having to sign on again (and without having to pay additional licences for our SSO service). It does seem MNet is the way to go for that and I know its fairly easy to set up as we already use it for our Moodle - Mahara links.
Richard