var someImages = new Array()
someImages[0] = 'images/headers/01.jpg'
someImages[1] = 'images/headers/02.jpg'
someImages[2] = 'images/headers/03.jpg'
someImages[3] = 'images/headers/04.jpg'


var j = 0
var p = someImages.length;

var preBuffer = new Array()
for (i = 0; i < p; i++){
   preBuffer[i] = new Image()
   preBuffer[i].src = someImages[i]
}

var whatImage = Math.round(Math.random()*(p-1));
function showPhotos(){
document.write('<img src="'+someImages[whatImage]+'">');
}