Running SharePoint on Windows Server 2008 R2 offers a wealth of possible SharePoint authentication scenarios. You are no longer limited to the basic, often unsecure authentication types.
In this article I will cover the SharePoint authentication methods, which closely mirror Windows Server 2008 R2 authentication scenarios since both SharePoint relies on Windows Server for much of its security. I will start with an overview of the primary authentication methods and then I will demonstrate how to configure authentication.
Excellent post from SharePoint Monitor
http://www.sharepointmonitor.com/2011/02/sharepoint-security-authentication/comment-page-1/
Aryan Nava 