Microsoft as released Enterprise Library 4.0.
You can download it here: http://www.codeplex.com/entlib
You can read about it here:http://blogs.msdn.com/agile/archive/2008/05/16/enterprise-library-4-0-for-visual-studio-2008-released.aspx
You can read about the new features here:http://msdn.microsoft.com/en-us/library/cc511712.aspx
You can read the online documentation here:http://msdn.microsoft.com/en-us/library/cc512464.aspx