var theImages = new Array() 

theImages[0] = 'images/id_ad_01.jpg'
theImages[1] = 'images/id_ad_02.jpg'
theImages[2] = 'images/id_ad_03.jpg'
theImages[3] = 'images/id_ad_04.jpg'
theImages[4] = 'images/id_ad_05.jpg'
theImages[5] = 'images/id_ad_06.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]+'">');
}