It’s possible to broadcast music, MP3, etc via Google Talk.  To do this:
Unplug your microphone.
Double click on the speaker icon in the lower right corner.
This will open up the “Volume Control”.
Now Select “Options”
Then “Properties“.
Check the button next to “Recording” – click OK.
You may also need to alter your setting under Mixer Device.
The Recording Control screen should be up.
Select “Wave Out Mix”. Click on the green phone in Google Talk and make your call.