window.onload = function(){
 var conf ={
   className : 'simg',
   endName : 'simg_end',
   postfix1 : '-b'
 };
 var imgNodeList = getElementsByClassName(conf.className);
 var node;
 var bimg = document.getElementById('homebimg');
 for (var i=0,len=imgNodeList.length; i<len; i++){
   node = imgNodeList[i];
   node.originalSrc = node.src;
   node.rolloverSrc = node.originalSrc.replace(/(\.gif|\.jpg|\.png)/,conf.postfix1+"$1");
   preloadImage(node.rolloverSrc);
   node.onmouseover = function(){
     bimg.src = this.rolloverSrc;
   };
 }
};

function getElementsByClassName(name){
 var elements = [];
 var allElements = document.getElementsByTagName('*');
 for (var i=0,len=allElements.length; i<len; i++){
   if(allElements[i].className == name){
     elements.push(allElements[i]);
   }else if(allElements[i].className == 'simg_end'){
     elements.push(allElements[i]);    
   }
 }
 return elements;
};

preloadedImages = [];
function  preloadImage(url){
 var p = preloadedImages;
 var l = p.length;
 p[l] = new Image();
 p[l].src = url;
}