You must assign a logon account for each of the Microsoft® SQL Server™ services. You may also specify whether the services should start automatically whenever you restart Microsoft Windows NT®. The SQLServerAgent service is dependent on the MSSQLServer service. You can autostart the SQLServerAgent service only if you autostart the MSSQLServer service as well.
You may enter one logon account for all of the services, or specify an account for each. The default account is the domain user account currently logged into the computer.
Note If you perform a custom installation and install the full-text search component, SQL Server Setup assigns the local system account to the Microsoft Search service and sets it to autostart. To change these options, run the Control Panel Services application.
Creating SQL Server Services User Accounts