Microsoft has recently updated BizTalk Developer Center at MSDN. BTS Developer Center can be entered here: http://msdn.microsoft.com/en-us/biztalk/default.aspx.
BTS 2009 Tutorials: http://msdn.microsoft.com/en-us/library/aa560270.aspx
BTS 2009 Documentation: http://msdn.microsoft.com/en-us/library/bb430723.aspx
Virtual Labs for BTS 2004, 2006 and 2009: http://msdn.microsoft.com/en-us/virtuallabs/aa740373.aspx
Best Practices Analyzer: http://www.microsoft.com/downloads/details.aspx?FamilyID=93d432fe-1370-4b6d-aaa8-a0c43c30f5ab&displaylang=en
BTS 2006 Installation and Upgrade guide: http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=9c697e02-d1bc-4684-8748-28b3a292d5bf