Program that lets the noise coming out of the speakers 'ACT' Like its a microphone input?

Well i play this games that has Mic Chat,However I do not have a microphone <. I was wondering if theres some program that makes the sound coming out of my speakers (ex. Music playing from my pc) Go into this ''Virtual microphone '' And transmitting the sound onto the game as almost if I have a mic and playing music. I tried ''rigging'' some cables but i cant seem to get anything to work :I