Look for some sheet music on the song of your choice. Store the 12 frequencies for one octave, than multiply accordingly (x2 for 1st, x4 for second, x8 for third, etc) to get any note in any octave. Make it as a function sound(note, octave). defines would be killer, such as Do = 0, Re = 2, Mi = 4, Fa = 5, etc..
Convert the sheet music in instructions for your theme.
Alternatively, you can get a midi and convert it.