When reading up on Kerberos security I found a nice tool that helps you with the tedious job of getting the Service Principal Names (SPN) right. It is called Kerberos SPN Viewer and Helper Tool. You can download it from msdn blogs. It was just released in a post a few days ago!
A good summary how Kerberos works, I found it in the following location: http://www.xml-dev.com/blog/?action=viewtopic&id=21 or as a Kerberos.
For the reasons why why we need SPN-s a quick introduction is written on Keith Guidebooks’ under: http://alt.pluralsight.com/wiki/default.aspx/Keith.GuideBook/WhatIsAServicePrincipalNameSPN.html. The PDF version of that page.