If this is XP Home, boot into safe mode and log on with the username Administrator, no / blank password.
If it's XP Pro, hit Ctrl + Alt + Del two times and then type Administrator into the username box and blank / no password
If this is XP Home, boot into safe mode and log on with the username Administrator, no / blank password.
If it's XP Pro, hit Ctrl + Alt + Del two times and then type Administrator into the username box and blank / no password