var theImages = new Array() 

theImages[0] = '../images/header2.jpg'
theImages[1] = '../images/header3.jpg'
theImages[2] = '../images/header4.jpg'
theImages[3] = '../images/header5.jpg'
theImages[4] = '../images/header6.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]+'">');
}