var theImages = new Array() 

theImages[0] = '_images/bigbanners/tour-01_1.jpg'
theImages[1] = '_images/bigbanners/tour-01_2.jpg'
theImages[2] = '_images/bigbanners/tour-01_3.jpg'
//theImages[3] = '400.jpg'
//theImages[4] = '500.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]+'" width="1000" height="323" border="0">');
}