Kerberos authentication

http://support.microsoft.com/kb/909801
OR
http://technet.microsoft.com/en-us/library/ee806870%28printer%29.aspx

You can use a command that is similar to the following to register an SPN for an instance:
SetSPN –A MSSQLSvc/.:1433
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How to make sure that you are using Kerberos authentication
After you connected to an instance of SQL Server 2005, run the following Transact-SQL statement in SQL Server Management Studio:

select auth_scheme from sys.dm_exec_connections where session_id=@@spid