If you didn't create an administrator account, when you created your current
Limited account, the original admin account disappeared. This account is
meant to be hidden and used only when the user created admin account cannot
be accessed.
In order to access that account, if you have XP Home Edition, boot to Safe
Mode, choose the account named Administrator, if you never created a
password for that account, leave the password blank and press enter. Then
go to Control Panel, User Accounts and create a new administrator account.
NOTE: you cannot name the account administrator. In order to boot to Safe
Mode, boot the system, start tapping F8, when the menu screen appears,
select Safe Mode and press enter.
If you have XP Professional, then at the Welcome screen, hit ctrl-alt-delete
twice and when the logon box appears, choose Administrator from the drop
down list or, if you don't see it listed, type Administrator, leave the
password blank, press enter and follow the instructions above.