KB 948465 - Windows Server 2008 Service Pack 2 Beta and Windows Vista Service Pack 2 Beta Download Links

Windows Server 2008 SP2 Beta and Windows Vista Service Pack 2 Beta apply to people, organizations, and technical enthusiasts who are comfortable evaluating prerelease software. This prerelease software is provided for testing only. Installation of Service Pack 2 Beta will result in Microsoft collecting information about the installation process, even if the installation is not completed. We do not recommend installing this software on primary or mission-critical systems. We recommend that you have a backup of your data before you install any prerelease software.

Windows Server 2008 Service Pack 2 Beta and Windows Vista Service Pack 2 Beta - Five Language Standalone
Windows Server 2008 Service Pack 2 Beta and Windows Vista Service Pack 2 Beta - Five Language Standalone for x64-based systems
Windows Server 2008 Service Pack 2 Beta and Windows Vista Service Pack 2 Beta - Five Language Standalone DVD ISO
Windows Server 2008 Service Pack 2 Beta and Windows Vista Service Pack 2 Beta - Windows Update Experience Kit

If you're curious what the registry key that the "Windows Update Experience Kit" adds, it is simply a REG_SZ of 93F7D954-DF91-22E6-99AB-4D8AF54E813A at:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate\VistaSP2\Beta1

Despite the warnings in the first paragraph above, this release works very well!