I found the WPF Overview Map at http://arcscripts.esri.com/details.asp?dbid=16871 very interesting, so I downloaded it, downloaded and installed ArcGIS Explorer and ArcGIS Explorer SDK. I opened the Visual Studio solution and tried to compile the solution, but I get the following error: The ArcGISExplorer SDK is not correctly installed - 'ESRI.ArcGISExplorer.targets' not found (ArcGIS_E3SDK='C:\Program Files\Explorer\DeveloperKit').
This issue has been seen before, although we do not have a fix, a reboot normally solves this problem (it seems that Visual Studio does not gain the environment variable correctly when the SDK is installed). See: http://resources.arcgis.com/content/kbase?fa=articleShow&d=37176
Let me know if that doesnt solve the problem for you.
