Windows Servers - Evaluate the Windows Server 2008 Public Beta 3
This from Microsoft: (it's dated April 25, but I just received the email)
"The next generation of the Windows Server operating system gives you more control, greater flexibility, and increased protection for your server infrastructure while reducing time and costs. And when you download or order the beta software, you're automatically registered to access valuable beta resources assembled in one convenient Beta Central location.
Please review Windows Server 2008 system requirements and compare editions before you proceed. Actual requirements and product functionality may vary based on your system configuration."
http://www.microsoft.com/technet/prodtechnol/beta/lhs/default.mspx