Gameboy MP3 player

i was wondering if anyone had done or had seen information on converting a gameboy (colour or advance into a portable MP3 player that could use the screen to display what song was being displayed etc. any information would be good. (even better if it had it all on a cartrige so that i could interchange them).

i was lookin gfor something like this because it would be an easier way than corrying them both around and plus at the moment i am absolutely flat broke (anybody want to donate? no...oh well than).

so if any one could help me it will be greatly appreiciated.

Thanks in advance

Kieran