Calling Executable at client End

Hello,

I want to call a Executable program at client using my web forms application. I have gone through posts and searched but can't find exact way to do it.
 Two examples that i think will relate to my current problem are
1. Way facebook video chat work, it just install it app at client end, and when client want to video chat , facebook is able to call its installed app.
2. Scott Hanselman at Dev Days 2010 demonstarated one example where he used to control his web cam using ASP.NET MVC app making call to COM component.
Thanks & Warm Regards
Anupam Misra.