Ive done basically the same project in year 8 but instead i used a picaxe programmer with ldr, and told it that when light from ldr drops below 10 than play music from buzzer. This was during christamss time and my parents had decorated the living room, soo i place the picaxe chip i programmed on one side of a doorway and a laser on the other side of the doorway which was pointed on the ldr. i also uploaded 3 christamss songs onto the chip.
so when someone walked through the doorway the lightbeam would break causing the ldr to sense lower light level and then play a christmas song (which would change everytime you walked passed it).
so this could also be done with your project you want to build. if you have got no knowledge of programming dont worry its very simple program and i can even help you. i soldered a picaxe chip together myself which reduced the price dramatically, so by doing a google search for picaxe should bring up a page on where to buy
Please contact me if you have any problems
hope i helped