Not ESB
This article's lead statement is that BizTalk Server is an Enterprise Service Bus (ESB).  In fact, BizTalk Server has always been positioned as an Enterprise Application Integration (EAI) server.  ESB is a layer on top of a Service-Oriented Architecture (SOA) and Microsoft provides these capabilities in BizTalk Server as a collection of components and documents in the "ESB Toolkit".  The ESB Toolkit is not part of the default installation of BizTalk Server and I therefore believe the opening statement of the article is misleading.Sir Crispalot