If you get following error:
This installation package could not be opened. Contact the application vendor to verify that this is a valid Windows Installer package.
to workaround this issue please take a look here:
http://forums.iis.net/t/1178551.aspx
Then you might get this error:
invalid Xml: element 'feed' is missing the required child element 'id'. What should I do to fix this to install my program?
Workaround is here:
http://answers.microsoft.com/en-us/windows/forum/windows_vista-windows_programs/i-am-trying-to-install-a-program-i-have-downloaded/c73c34d6-e034-4e79-8a08-59feb94f5cf4?page=2