Microsoft just released BizTalk Server 2009. It is the sixth release of this product. Here is a list of handy resources about BizTalk 2009.
Technical Overview
Installation and Upgrade Guides
Hyper V Guide
Scale Out Poster
Scale Out Interactive Poster
Database Infrastructure Poster
BAM Poster
BizTalk 2009 Hands On Virtual Labs
http://msdn.microsoft.com/en-us/virtuallabs/aa740373.aspx
Infrastructure Planning and Design