If you’re interested in how the worlds of Web Services and BizTalk Orchestrations come together, check out this article I wrote a while back. It’s called Implementing Service Contracts with BizTalk Server 2004.
It focuses on the issues around mapping between these two worlds, how to implement existing WSDL definitions in a BizTalk orchestration, what happens when you use the WS publishing wizard, etc.
I had completely lost track of this article because it never showed up on the MSDN Web Services Developer Center (where it was originally intended), and I recently learned that it ended up within the BTS 2004 technical articles section on MSDN instead. Anyway, some of the content might be a bit stale if you’re using BTS 2006 but the general principles still apply. Let me know if you have any feedback.