Actually if you are interested in making music and noise with the Arduino, you don't need anything else except perhaps a small breadboard, find a speaker from somewhere, and you are almost there. You can just "bit banging" to make sound, or use a R2R ladder. Check out these links as a starting point:
http://www.uchobby.com/index.php/2007/11/11/arduino-sound-part-1/
Basically by switching one output pin on and off, you can start making sound.
P.K.