BizTalk Server 2006 Beta 1 is available through Microsoft Beta program.
There are a lot of great improvements in the areas that were painful in the previous version such as biztalk solution deployment, management. Also some new features like BAM Portal, Business alerts, Flat file import wizard, recoverable interchange processing in pipelines.
So, if You are working with BizTalk and have some time to play with betas (You should have some ), then go to the https://beta.microsoft.com, sign in with the passport and sign as guest using BizTalkBetaTeam as your guest ID.