lastScrollY = 0;
function heartBeat(){ 
var diffY;
if (document.documentElement && document.documentElement.scrollTop)
diffY = document.documentElement.scrollTop;
else if (document.body)
diffY = document.body.scrollTop
else
    {/*Netscape stuff*/}

//alert(diffY);
percent=.1*(diffY-lastScrollY); 
if(percent>0)percent=Math.ceil(percent); 
else percent=Math.floor(percent); 
document.getElementById("leftDiv").style.top = parseInt(document.getElementById("leftDiv").style.top)+percent+"px";
document.getElementById("rightDiv").style.top = parseInt(document.getElementById("leftDiv").style.top)+percent+"px";

lastScrollY=lastScrollY+percent; 
//alert(lastScrollY);
}

//下面这段删除后，对联将不跟随屏幕而移动。
window.setInterval("heartBeat()",1);