I am 90% sure NTUSER.DAT is one of the profiles for a user in XP. What the RMBAK is I will have to leave for someone with more knowledge than me. Open up control panel and go to users and see if there is another user other than administrator and any others you may have added.If you have added the .NET framework this I think adds another user on its own. Or at least it did when I installed it. May be way of centre here but it is all I can think of.