The changes to the built-in administrator account in Windows Vista

A good KB writeup about the changes that went into Vista and the built-in administrator account.

Short summary:
By default, the built-in administrator account is named Administrator. Additionally, the built-in administrator account is assigned the relative ID (RID) 500. In Windows Vista, the default user account type is a standard user. A standard user is a user who has limited account rights and limited Windows permissions. The following sections detail how the built-in administrator account has been changed to better reduce the potential attack surface of the built-in user accounts in Windows Vista.