Information and issues with Kerberos security within SQL Server 2005?

What is the Kerberos Authentication? 

What are the security features difference between Windows 2000 and 2003 versions?

How it is behaved within Failover Clustering?

How to enable Kerberos Authentication Including SQL Server Virtual Servers on Server Clusters?

Let us see how the user access to SQL Server resources is controlled by two separate mechanisms. The first one is authentication, which determines the identity of a user attempting to connect, based on a verifiable identifier. The second one is authorization, which establishes the level of privileges granted to a login associated with the logged on user. 

On the Security perspective windows domain environment provides a number of additional advantages over SQL Server authentication mechanism. Local & Domain accounts implement account policies, enforcing password complexity, maximum and minimum age, history, as well as lockout settings. This is basic security but more on this the highest level of security is provided by Kerberos authentication, which requires that login accounts reside in a Windows 2000 or 2003 native mode Active Directory domain and that client computers run Windows 2000 or later.  You need to ensure that servers communicate using TCP/IP Net Library, since this is the only one which supports Kerberos based authentication. I would say refer to this KBA319723 for complete information on Kereberos authentication.