随滚动条动的图片

<style type="text/css">
#main{text-align:center;}
#adver{
 position:absolute;
 left:50px;
 top:30px;
 z-index:2;
}
</style>
<script type="text/javascript">
var adverTop; //层距页面顶端距离
var adverLeft;
var adverObject; //层对象
function inix(){
   adverObject=document.getElementById("adver"); //获得层对象
   if(adverObject.currentStyle){
   adverTop=parseInt(adverObject.currentStyle.top);
   adverLeft=parseInt(adverObject.currentStyle.left);
}
else{
 adverTop=parseInt(document.defaultView.getComputedStyle(adverObject,null).top);
   adverLeft=parseInt(document.defaultView.getComputedStyle(adverObject,null).left);
 }
}
function move(){
adverObject.style.top=adverTop+parseInt(document.documentElement.scrollTop)+"px";
adverObject.style.left=adverLeft+parseInt(document.documentElement.scrollLeft)+"px";
} 
window.onload=inix;
window.onscroll=move;
</script>