sorry for not reacting on your answers. but yet i have almost no idea how your solutions will work.
first i've got to read about midi and also about the meta file format that was mentioned to proberly understand what you mean.
the first solution seems to need a PC, right?
the second solution i dont get 
@juergen... yes this i s my song. i have one final mix and one mix where i've panned the channels for the movement
do you think that it's possible and easy to use ONE mp3player (f.e. from Sparkfun). and create a real button. if the button is pushed than TWO songs were played at the same time. without using PC. the first song goes into the arduino via "shitfy vu shield". the second one goes to the headphones or speakers..
but that would mean that i need a mp3player that has two stereo outputs
or... i use two mp3 shields that get started by a button at the same time... hmpf... brainf$%&ing^^