function newImage(arg) {
	if (document.images) {
		rslt = new Image();
		rslt.src = arg;
		return rslt;
	}
}

function changeImages() {
	if (document.images && (preloadFlag == true)) {
		for (var i=0; i<changeImages.arguments.length; i+=2) {
			document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
		}
	}
}

var preloadFlag = false;
function preloadImages() {
	if (document.images) {
		mbf_03_over = newImage("nav/mbf_03-over.gif");
		mbf_04_over = newImage("nav/mbf_04-over.gif");
		mbf_05_over = newImage("nav/mbf_05-over.gif");
		mbf_06_over = newImage("nav/mbf_06-over.gif");
		mbf_07_over = newImage("nav/mbf_07-over.gif");
		mbf_08_over = newImage("nav/mbf_08-over.gif");
		mbf_09_over = newImage("nav/mbf_09-over.gif");
		mbf_14_over = newImage("nav/mbf_14-over.gif");
		mbf_15_over = newImage("nav/mbf_15-over.gif");
		mbf_16_over = newImage("nav/mbf_16-over.gif");
		preloadFlag = true;
	}
}

<!-- Begin

var theImages = new Array()

theImages[0] = 'img_rand/01.jpg'
theImages[1] = 'img_rand/02.jpg'
theImages[2] = 'img_rand/03.jpg'
theImages[3] = 'img_rand/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]+'">');
}

//  End -->