Multicasting

Anyone knows how to do multicasting with C++/MFC ?

I want to do a voice chat program, and when I have a lot of people connected it's too much data to send over the internet... I have to send the same data to 2 or more people...
My program could work so much better if I could add something like multicasting to it.

There was an article on Multicasting on http://www.gamedev.net/ about 6 months back. Take a browse through their features archive.

Z.