Live audio playback

I've been trying for ages, to no avail, to get my pc to play sounds while I stream things IE I play a movie on something and stream the video and audio. Instead it always attempts to record my microphone and, oddly, I have no stereo mix. The only thing that appear on, for example, audacity when I try and change the recording device are my microphone and "Microsoft sound mapper"
Incase it helps to know I don't have a sound card.

Forgot to mention that I would like help on how to stream audio :p