If you are reading the upgrade documentation
(Upgrading to BizTalk Server 2006 R2 from BizTalk Server 2006.doc)
“To apply the HIPAA33ForR2.mst transform”
You can download the Windows SDK from http://go.microsoft.com/fwlink/?linkid=75636
That link doesn’t work, you need to go here and choose the right environment:
http://msdn2.microsoft.com/en-us/windowsserver/bb980924.aspx
Thanks windows SDK blog for the quick turn around!