Google Talk’s First “Hack” - Share MP3’s, Podcasts, and More!
The following is not exactly what you could call a hack, more like a trick rather, but nevertheless its an excellent way to share your podcasts and stream music while chatting to your buddies over GTalk. Thanks to ‘manatee‘ over at TwitTV for the heads up:

For PC’s (Tested on Windows XP & Windows 2000)Step 1: If you have a mic plugged in, unplug it
Step 2: Double click on the speaker icon in the lower right corner. This will open
up “Volume Control”. Select “Options” and then “Properties”. Then check the button
next to “Recording” then click OK. You may also have to change your setting under
Mixer Device.
Step 3: Now the Recording Control screen should be up. On my computer I selected “Wave Out Mix”
Finally, you might just need to play around as each PC is going to be a little different.
The best way to get it to work if you’re having trouble is to call a friend on your messenger and simply play around with the settings until they hear music or you see the microphone equalizer moving around in the chat window on your end.
Now if you haven’t launched Google Talk yet, go ahead and do that and try calling a friend. Click on the green phone icon to call them. If you see the microphone equalizer thing moving on your end, the other end should hear music, your podcast, or whatever.
For more Google Talk hacks/mods, please visit the GTalk forum over at GoogleCommunity.

