Huh? iTunes is the media player. I'll take a stab and guess your friend has music in AAC (with the .m4a container), perhaps purchased from the Apple Store? If so, iTunes itself can do this by going to iTunes' preferences (from Edit > Preferences) and clicking the Import Settings button under the General section. From there set Import Using to MP3 encoder and if the music was purchased from the iTunes store you'd want to at least set the Setting to Higher Quality (192kbps) or customize it to 256kbps or 320kbps. With all that set you can right click the music file(s) in iTunes and select Create MP3 Version and let iTunes do its thing.