After you've renamed the Main account to Administrator you should try and boot witht the XP CD and access the Recovery Console.
It will ask you to logon as the Administrator with the password.
This test will see if the Administrator account is recognized by XP as the valid account to use.
Also for XP Home Edition Ctrl+Alt+Delete twice will not let you logon as Administrator. That method is for XP Pro.
You'll have to restart and hit F8 and boot into Safe Mode to logon as Administrator.