Have done this to hosting service but it does not seem to have taken over from the Wordpress database already there - our Atahualpa theme still looks the same.

It does not show 'Site Admin' or 'Attributes' on 'Pages' to set up page order as per instructions on here - assume that is with MU version.

Would it be best to delete our database and re-install WPMU then start rebuilding our site all over again?

Thanks in anticipation.

When installing WPMU you'd have to tell the database name at some point. Usually you'll use another, new database for WPMU. Then there shouldn't be any conflicts