I was reading through an unrelated thread and found this,
"gpalmer711 (IS/IT--Manageme) Apr 20, 2004
When you first install windows XP the Administrators password is blank. You could Try logging on with the user name administrator and no password. If you are at the Windows XP Welcome screen where no Administrator user is visible then tap Ctrl-Alt_Del twice at the welcome screen and the standard network login dialog will appear.
Greg Palmer"
Hope this solves your problem.
Brett.