Ummmm.... No
It is not possible to remove the vocals from a song completely.
Thats unless you have the Multi Track master from the recording studio, then yes. But that is never released to the public, it stays with the recording studio or recording company. That unless you get permission to do a remix of a song and the artist releases the track breakdown to you.
It is possible with some hardware devices such as a pro-logic audio amp to soften the vocal frequency's for Karaoke, this is done if you are watching a stereo film on a pro logic amp, and the vocals are put through the centre channel, but there is always seepage into the left and right speakers unless you are watching a DVD that has a multi track soundtrack.
So Short answer, the only software you might find would 'muffle' the vocals of a song (and not very well) and I don't know of any software that would do this. But there is no way to completly remove the vocals off a audio file from the instrumental =]