The ESB Guidance for BizTalk Server 2006 R2 has been released and is now available here on the Patterns & Practices web site.
The ESB Guidance provides architectural guidance, patterns & practices, and a set of BizTalk Server 2006 R2 and .NET components to simplify the development of an Enterprise Service Bus (ESB) on the Microsoft platform and allow Microsoft customers to extend their own messaging and integration solutions.
There's a lot of information to wrap your head around, and it's certainly no small undertaking to implement a full ESB within your enterprise. This, however, should make taking those steps toward implementing one much easier, even if you just start with some small piece of it and expand it later on.
The management portal alone makes it worth taking a look at this. We also have full integration with SOA Software and Amberpoint solutions for managing, securing and instrumenting your services.
ESB Guidance: http://msdn2.microsoft.com/en-us/library/bb931189.aspx
ESB Guidance Community site: http://codeplex.com/esb