Windows Vista Service Pack 2 Beta Available for Public Download
Windows Vista Service Pack 2 Beta, which was made available available to Technet/MSDN Subscribers, is now available for public download from the Windows Vista Service Pack 2 Beta Customer Preview Program (CPP) Website.

Important: This prerelease software is provided for testing only. It’s not recommended to install Beta software on primary or mission-critical systems.

To install Vista Service Pack 2 Beta on a single computer, use the Windows Update applet. Prior to that, you need to run a command script from Microsoft, that will set a registry key on your computer that will enable Windows Update to offer you the Service Pack. To download the command script and Vista SP2 CPP documentation, visit Windows Vista Service Pack 2 Beta - Windows Update Experience Kit page.

The command script does the following:

1. Deletes these two keys.
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion \WindowsUpdate \VistaSP2

2. Adds a String value named Beta1 in the following registry key (which is re-created), and sets 93F7D954-DF91-22E6-99AB-4D8AF54E813A as its Value data.
Installing Vista Service Pack 2 Beta

Before installing SP2 Beta via WU, you need to install a prerequisite update, and all other "important" updates for Windows Vista. For detailed information on installing Windows Vista SP2, refer the file WUReleaseMessage_CPP_WS08VistaSP2.docx. If you don’t have Office 2007 or Office 2007 Viewer installed (needed to view .docx files), use the RTF version of the file that I’ve uploaded here.
Standalone Package

If you’re going to install Windows Vista SP2 in multiple computers, then get the Standalone package from this link.

Vista SP2 Beta - Five Language Standalone (KB948465) [File size: 388.3 MB]