General CADD Pro has released a free extension to Google Desktop Search (GDS) that allows the user to find DWG and DXF files with specific text strings. The add-on also searches for text inside General CADD GXD files.
Autodesk offers Google Desktop Search compatibility starting with AutoCAD 2006, using its iFilter technology. The advantage of using General CADD’s extension to GDS is that users of older version of AutoCAD can now also search inside their DWG and DXF files.
For several months I ran both Google Desktop Search and Microsoft's MSM Desktop Toolbar side-by-side. I eventually removed the Microsoft search tool. It was slower to generate results, and relied too heavily on Microsoft applications to display search results. Google Desktop Search, by comparision, displays search results in a browser window.
More information: http://www.generalcadd.com/plugin-1.htm
--RSN