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("floatad1").style.top=parseInt(document.getElementById("floatad1").style.top)+percent+"px";
//document.getElementById("floatad2").style.top=parseInt(document.getElementById("floatad2").style.top)+percent+"px";

lastScrollY=lastScrollY+percent;
//alert(lastScrollY);
}
window.setInterval("heartBeat()",1);

//<div id="floatad1" style="left: 10px; position: absolute; top: 200px;"><a href="#" target="_blank"><img src="images/ad1.jpg" /></a></div>	左侧广告
//<div id="floatad2" style="right: 10px; position: absolute; top: 200px;"><a href="#" target="_blank"><img src="images/ad2.jpg" /></a></div>右侧广告
//<script type="text/javascript" language="javascript" src="http://WebEffect.bbcwx.com/onlineservice/floatad_couplet.js"></script>