Lots of technical content is already recorded. Start with the first web-cast below if your customer is new with BizTalk Server.
MSDN Webcast: Real-World BizTalk Server 2004 Editing and Mapping Techniques
MSDN Webcast: Building on BizTalk Server 2004 Human Workflow Services for the Visual Studio .NET developer
MSDN Webcast: BizTalk Server 2004 EDI with and without the Covast Accelerator
MSDN Webcast: InfoPath SP1 and BizTalk Server