To the SharePoint : Enabling Kerberos authentication for an Office SharePoint Server 2007 farm deployment

Here's another little nugget in the never ending struggle to kerberize your SharePoint implementation - Kerberos authN against the SSP infrastructure:

The Infrastructure Update for Microsoft Office Servers includes a new, custom-format SPN for Kerberos authentication for the SSP infrastructure. This custom-format SPN introduces a new Service Class: MSSP. The custom-format SPN uses the following format: MSSP/<host:port>/<SSP name>. This new custom-format SPN sets a .NET Framework property to direct the .NET Framework to use a specific SPN for a given URI. The .NET Framework is used to make inter-server calls to the Office SharePoint Server 2007 SSP infrastructure Web services. 

I highly recommend taking a look at this article and the subsequent reference documentation - Configure Kerberos authentication (Office SharePoint Server).

To the SharePoint : Enabling Kerberos authentication for an Office SharePoint Server 2007 farm deployment