In the Control Panel > Administrative Tools > Computer Management >
Local Users and Groups > Users you can change the status of the users
on this computer.
Simply log in using the built-in Administrator account (which
_cannot_ be deleted) and modify the desired account. By design, the
only way to log into the Administrator account of WinXP Home is to
reboot into Safe Mode. For WinXP Pro, pressing CTRL+ALT+DEL twice at
the Welcome Screen will produce the standard login dialog box.