If you're getting an error with error code 2869 when installing the sample preview handlers associated with my preview handler article from the January 2007 issue of MSDN Magazine, make sure you're following the directions in the README file.  Open a new console window with "Run as administrator".  From the console window, change to the directory containing the MSI, and execute the Install.bat file in the same directory.  That .bat file will in turn launch msiexec with the MSI for the preview handlers, and everything should install just fine.  See http://blogs.msdn.com/donsmith/archive/2006/11/30/installing-software-factories-on-vista.aspx for more information; in short, though, this is due to interactions with User Account Control (UAC).