Steps to integrate Sharepoint and BizTalk?

Indeed, BizTalk 2006 ships with an out-of-the-box WSS adapter (see here for more on it .. http://www.microsoft.com/biztalk/techinfo/whitepapers/adapterwp.mspx).  This adapter allows you to both poll document libraries in a SharePoint site, and push messages to document libraries (and technically "lists" as well).  It's fairly easy to set up, as BizTalk uses the SharePoint web services interface.  There are some security considerations that are included in the installation docs.

 Note that this is SharePoint 2003, NOT MOSS 2007.  You'd have to tweak the existing adapter to work with the new SharePoint version. 

Besides using the Sharepoint adapter, which enables you to:
 – receive and send documents from/to WSS document libraries and form libraries
 – document filtering based on WSS views
 – archiving of documents
 – promoting of document properties,

you can deploy BizTalk orchestrations as web services and use SharePoint DataViews to show the results of the web service calls.
However keep in mind that BizTalk is not (yet) your best choice when it comes to realtime processing. So when it comes to show data in SharePoint which comes from BizTalk orchestrations, it's best to deploy only simple/fast orchestrations as web services.

More information about the WSS adapter can be found at the blog of Adrian Hamza (http://blogs.msdn.com/ahamza/default.aspx).