Today, Microsoft offers at least two different tools for searching the desktop.
One of them, targeted at consumers, is the MSN Search toolbar. You can download it at no cost from http://toolbar.msn.com. If you need information on how to deploy this tool in a company setting, check the Administrator Guide at http://www.microsoft.com/technet/prodtechnol/windows/search/tbguide.mspx
Another tool is the Windows Desktop Search (WDS), which is targeted at enterprises that need a flexible tool for the company desktop. This version includes support for multiple languages, deployment via Group Policy and even a complete SDK for customization. You can find more details and a free download at http://www.microsoft.com/windows/desktopsearch/enterprise
Both the MSN Toolbar and the WDS are provided for Windows XP and Windows 2000.
In Windows Vista, however, search won't be a tool that you deploy after you load the OS. It will be already there, front and center. Actually, it will be at the top right (that's consistently where you will find the search box in the Windows Vista OS and the tools that come with it).
The Search capabilities in this new OS goes above and beyond what you can do today with the Windows Desktop Search or the MSN Search Toolbar. You can read more about it at:
http://www.microsoft.com/windowsvista/features (make sure you click on the "Search and Organization" link on this page) and also at http://msdn.microsoft.com/windowsvista/discoverable (scroll down to the
"Full Text Search" item on this page).