function popwin(theURL,winName,features) { //v2.0
  window.open(theURL,winName,features);
}


<!-- This script and many more are available free online at -->
<!-- The JavaScript Source!! http://javascript.internet.com -->
<!-- Begin

// Set up the image files to be used. >> SET THE ARRAY pre-header for each page as needed
//var theImages = new Array() // do not change this

//theImages[0] = '/images/orpheus-01.jpg'
//theImages[1] = '/images/orpheus-02.jpg'
//theImages[2] = '/images/orpheus-03.jpg'
//theImages[3] = '/images/orpheus-04.jpg'

// 

var j = 0
var p = theImages.length;
var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = theImages[i]
}
var whichImage = Math.round(Math.random()*(p-1));
function showImage(){
document.write('<img src="'+theImages[whichImage]+'" />');
}