If it can be AS2, copy this to an empty fla, then import 5 sound and set their linkage identifiers sound0 to sound4. I'd be happy to explain the code to you if this is what you need. If it can't be AS2 and has to be AS3, good luck. You can probably learn from this and change it to AS3 though.
var keyListener:Object = new Object();
keyListener.onKeyUp = function ()
var sound:Sound = new Sound();
sound.attachSound("sound" + getRandomNumber(0, 4));
function getRandomNumber(min:Number, max:Number):Number
return (Math.floor(Math.random()*(max-min+1)) + min);