PC Speaker beep via javascript?

Try following way: It may easy for you....

function play_beep() {
  var snd = new Audio("http://www.externalharddrive.com/waves/computer/hello.wav");
  snd.play();
  return false;
}

<input type="submit" value="Play Beep" onclick="return play_beep();" />

It's possible with JavaScript today.

Here's a quick & dirty function I wrote...

var beep = function(duration, type, finishedCallback) {

    if (!(window.audioContext || window.webkitAudioContext)) {
        throw Error("Your browser does not support Audio Context.");
    }

    duration = +duration;

    // Only 0-4 are valid types.
    type = (type % 5) || 0;

    if (typeof finishedCallback != "function") {
        finishedCallback = function() {};   
    }

    var ctx = new (window.audioContext || window.webkitAudioContext);
    var osc = ctx.createOscillator();

    osc.type = type;

    osc.connect(ctx.destination);
    osc.noteOn(0);

    setTimeout(function() {
        osc.noteOff(0);
        finishedCallback();
    }, duration);

};

jsFiddle.

Using JavaScript, it's impossible - JavaScript has no access to the client computer except cookies and the new HTML5 local storage.

What you can do, however, is use a Java applet that will be controllable via JavaScript - hidden or not.

You can find an example here.

This requires Java runtime to be installed on the client computer.