Your problem doesn't sound that complicated,and is easily doable. You have separate audio, and video streams, and you want to combine them and stream it, right ?
Simplest way will be to use either windows media encoder or adobe media encoder. Windows media encoder do have the additional capability of streaming the video straight, without a streaming server involved. You can select your webcam as 'source video' and select any microphone as 'audio source', and windows media encoder will combine both of them, and create a stream for you, which can be watched live by anyone, or could be pushed to a streaming media server for relay broadcasting.
Link to wme http://www.microsoft.com/en-in/download/details.aspx?id=17792