Is there a software that can play music as mic input?

is there any software out there (preferably free) that allows you to play music as your mic input, I know you can use your sound card but then for things like ventrilo there is either echo for other people or I have to mute them so i cant hear feedback. I would prefer a software that can play an mp3 or wav or any other music file as my mic input but if you can help me with my more specific ventrilo problem that is ok too