Arduino and mp3 player

Thanks everyone. I realize this may not be the best way to do things, but does anyone have any ideas on how to trigger a sound device via arduino without buying any special boards (sheilds, etc) or communicating with the player via serial (because I think that requires some sort of serial break out board and/or taking apart the mp3 player, right?

Sorry, new to all this arduino stuff (but it is very very cool)