This paper proposes to use the techniques of Music Information Retrieval in the context of Music Interaction. We describe a system, the SongSampler, inspired by the technology of audio sampling, which automatically samples a song to produce an instrument (typically using a MIDI keyboard) that plays sounds found in the original audio file. Playing with such an instrument creates an original situation in which listeners play their own music with the sounds of their favourite tunes, in a constant interaction with a music database. The paper describes the main technical issues at stake concerning the integration of music information retrieval in an interactive instrument, and reports on preliminary experiments.