If you are in the process of evaluating the Biztalk 2009 (the Microsoft platform for EAI, B2B and BPM) you might be interesting in reading the "Microsoft BizTalk Server 2009 Technical Overview" whitepaper and the "Understanding BizTalk Server 2006" whitepaper by David Chappell, that is still a valid document to provide an overview of the latest Biztalk platform. Finally, if you want to quickly try out a fully installed and configured instance of Biztalk 2009, download the virtual machine over here. The VM has everything you need to evaluate the product (BizTalk Server 2009, SQL Server 2008, SharePoint Server 2007, Microsoft .NET 3.5 framework and five hand-on-labs).