Windows Vista Service Pack 2 Beta and Windows Server 2008 SP2 beta are available to download from Microsoft Download center. Few days back it was released for MSDN and Technet subscribers and from yesterday it is available for general public. This update is available to users who have any of these languages: English, German, French, Japanese or Spanish.
Download Five Language Standalone file, If you wish to download using Windows Update you can find the file here>
More information on Service pack 2 is available here, Frequently asked questions regarding this pack can be accessed here. Release notes for Windows server 2008 SP2 beta can be accessed from here and release notes for Vista SP2 can be accessed from here.
You need to have SP1 installed before installing SP2. Remember if you install this beta release you need to uninstall it before installing SP2 final when it is released. Vista SP2 final release won’t come until first half of 2009 according to Microsoft. If you have installed release candidates previously you need to uninstall them before installing SP2.
Read this note before installing SP2 Beta
Windows Server 2008/Windows Vista SP2 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.