You won't find the Administrator account in the User Accounts in Control Panel. By default Administrator account is present but it is hidden and disabled on all clean installs of Vista operating system. There are two ways to access the Administrator account in Windows Vista.

Unlike previous versions of Windows, there are differences in Vista between accounts with "computer administrator" privileges and the Administrator account. For example, the Administrator account does not have User Account Control enabled.

The two methods and more details can be found here.