Thanks Cactus for your response
Domain mode: I was trying to avoid this route because as there is a lack of experience around here with this, and I myself am leaving here later in the year.
New user account: I thought I might have been confusing with my terminology, but that is what Windows calls them - I can create a new user account on the Windows machine and if I give it the same u/n and p/w as the SME server, then it will logon automatically to the SME server. But if I simply try and change the name of an existing user account in Windows, it doesn't work, as it doesn't change all the related registry entries.