first create a new user account in xp,through user accounts.
go to RUN type regedit open key "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\W
In the right side u can see list just right click in empty area and select a new DWORD
value. and rename it to your user account's name(user name).
just close registry press F5(refresh) and go to your user account what u see.......
wow! your account is not displayed in user account.
Now u can't see your account in logon screen so how to access it , just press ctrl+alt+del twice a new window opens enter your username and password(if not set leave it blank).