I'm... not quite sure how to respond to that.
A quick Google search for "creating masks in Sony Vegas" yielded a couple of tutorials. I'd check them out and see if you have the same tools in your version that they're using. If you do, once you know how to use them, it'll be easy enough to adapt it to fit your purpose.
Be careful, though. Anything but a straight-on shot seems like it would be pretty difficult to do, especially if the head is turning mid-speech.
With all due respect Noodle, I don't want you here. - Ratboy Productions