BizTalk includes some limited support for EDIFACT. For example, with the BizTalk Editor you can define a NEW document, it will then give you a choice of a blank specification, EDIFACT, X12 or XML specifications. Choose the EDIFACT spec and then the sub-folder for the EDIFACT directory you want (not all EDIFACT directories are provided) and then the document type you want (again, not all documents are provided). This will give you the basic BizTalk specification for an EDIFACT document. If you cannot find exactly what you want, you may be able to create what you need by editing the specification created from one of these basic templates.
Having said all that, we don't use BizTalk for dealing with the raw EDI documents, we use third-party software to convert from/to EDI formats and XML, as BizTalk does not support some key EDI features that we need.
Hope this helps a bit, but I suspect you're going to have a lot of fun with EDI. ;)