What you do is open up your webcam, press record on your game capture as soon as that starts, then, when done, just stop recording both. I have a crack for Sony Vegas Pro, and when you open that, open up the webcam video FIRST, then open the game video, drag the game video under the webcam video, and then press the little box at the end of the webcam video, then shrink it. Here's a video (Probably a lot better than my reply. :P)
youtube.com/watch?v=NPIFswLFgM4