var theImages = new Array() 

theImages[0] = 'images/random/1.jpg'
theImages[1] = 'images/random/2.jpg'
theImages[2] = 'images/random/3.jpg'
theImages[3] = 'images/random/4.jpg'
theImages[4] = 'images/random/5.jpg'
theImages[5] = 'images/random/6.jpg'
theImages[6] = 'images/random/7.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]+'">');

}