function swapimage() { 
theimages = new Array("images/left-banner-1.jpg",
"images/left-banner-2.jpg",
"images/left-banner-3.jpg",
"images/left-banner-4.jpg",
"images/left-banner-5.jpg"); 
whichimage = Math.floor(Math.random()*theimages.length); 
document.write('<img src="' +theimages[whichimage]+ '" alt="">'); 

}