In Windows 7, you would to the following, it's probably similar in Vista (I've not tried Vista).
- right-click the audio icon in the system tray, select recording devices.
- right-click Rec Playback and select it as the default device.
The mic is selected by default, and that's why you stream the mic.
Broadwave will stream whatever you play, as selected in the recording devices. Rec Playback means whatever is selected in the Playback, and will play Windows Media Player, iTunes, etc.