Windows Desktop Search (WDS) 3.0 is a native component of Vista, and is being shipped separately as a system component for Windows XP and Windows Server 2003 users. WDS is a system service that indexes file, email and other content in order to provide fast searches over content and properties. It is an upgrade to all previous 2.x versions of Windows Desktop Search you may currently use. Outlook 2007 will have a new version of Instant Search technology that is built on top of WDS and is dependent on its presence for search to work.
The Beta 2 Technical Refresh of Outlook will prompt you to download and install a new version of Windows Desktop Search 3.0 if you are running on WinXP. This is required in order to support our new Instant Search capabilities in Outlook.
"Windows Desktop Search 3.0 (WDS) enables fast search on your computer using indexing technology. It helps you to find your documents, email, music, photos and other items. The search engine in Windows Desktop Search 3.0 is a Windows service that is also used by applications such as Microsoft Office Outlook 2007 and Office OneNote 2007 to index application content and deliver instant results when searching within an application.
This release is an update to the Beta Engine Preview release of Windows Desktop Search 3.0. The most noticeable improvements include full Desktop Search UI, 64-bit support, and better performance. The installation process will automatically upgrade 2.5 and higher versions of Windows Desktop Search. Earlier versions of Windows Desktop Search should be uninstalled from Add/Remove Programs before this version is installed."
The download button will take you to this page for installation. If you're running a 64bit machine you can find the WDS build on this page instead.
If you're running on Vista RC1 or later, you'll be good to go with no separate installation needed. J