Technet provides a programme for the latest betas and downloads that provides you a one-stop ship for all of these as well as supporting information. Here are the latest:

With Microsoft BizTalk Server 2006 R2, you can connect to .NET applications and infrastructure with your non-.NET applications and platforms, as well as those of your partners. And when you download the 120-day trial software, you’re automatically registered to receive valuable resources delivered at strategic intervals throughout the software evaluation period.

Microsoft System Center Virtual Machine Manager 2007 is a comprehensive solution optimized for the management of Microsoft Virtual Server 2005 servers running in the virtualized data center. When you download the 120-day trial software, you’re automatically registered to receive valuable resources delivered at strategic intervals throughout the software evaluation period.