I am trying to set my htaccess file so that when a user clicks on a link it opens a download dialogue box and when the user clicks on open iTunes.exe is opened and the file is processed. File extension is pcast

I've figured out how to force the download process to happen using application/octet-stream pcast. but I can't get iTunes to open from the dialogue box

podcasts.yahoo.com has been able to make this work

Anybody have any idea how yahoo is making this work??