Enable Administrator account in Windows

When you install Windows XP, Vista or Windows 7, windows asks you to create a user account. When you try to create an account with the user name "Administrator", Windows tell you that you can't do this, because this account already exists by default but is disabled.
At this point you can create, an account with a different user name than "Administrator" and when you log on in Windows, you want to enable the built in "Administrator" account.
Following the below process you can do this.