Registering a Service Principal Name
http://msdn.microsoft.com/en-us/library/ms191153.aspx
How to use Kerberos authentication in SQL Server
http://support.microsoft.com/kb/319723
Service Principal Name (SPN) Support in Client Connections
http://msdn.microsoft.com/en-us/library/cc280459.aspx
and the complete article
What SPN do I use and how does it get there?
http://blogs.msdn.com/psssql/archive/2010/03/09/what-spn-do-i-use-and-how-does-it-get-there.aspx