BizTalk Server 2006 Beta 2 is available for registration and then download.
- Go to http://beta.microsoft.com and log in with your MS Passport account.
- Click on "Sign in as Guest" and use this Guest ID: BizTalkBetaTeam.
- On the left side, under "Program Info," click on "Survey" and complete the nomination form, and submit it.
You should subsequently receive a confirmation email with further information about downloading hte beta, newsgroups, etc. After you've received that letter, you'll be able to download the good bits.