function MoveLayer(layerName) { 

var y = 100;//浮动广告层固定于浏览器的y方向位置
  
var diff = (document.body.scrollTop + y - document.all.AdLayer.style.posTop)*.90;

diff=(diff>0?1:-1)*Math.ceil(Math.abs(diff));

var y = document.body.scrollTop + y - diff; 
eval("document.all." + layerName + ".style.posTop = y");
setTimeout("MoveLayer('AdLayer');", 20);//设置20毫秒后再调用函数MoveLayer()
}