window.onload=function(){  
   var thediv=document.getElementById("freakyCreatures");  
   var imgarray = new Array("/images/freaky_creatures_bg.jpg", "/images/freaky_creatures_bg1.jpg", "/images/freaky_creatures_bg2.jpg");  
   var spot = Math.floor(Math.random()* imgarray.length);  
   thediv.style.backgroundImage="url("+imgarray[spot]+")";  
}