为什么我的js对联广告代码一到xhtml1.0里面就不滚动了！

document.body
-->
document.documentElement<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html><head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>新建网页 1</title>
</head><body>
<script language="javascript">
<!--
var   delta=0.15;
  var   collection;   
  function   floaters()   {   
  this.items   =   [];   
  this.addItem   =   function(id,x,y,content)   
  {   
  document.write('<DIV   id='+id+'   style="Z-INDEX:   10;   POSITION:   absolute;   width:80px;   height:60px;left:'+(typeof(x)=='string'?eval(x):x)+';top:'+(typeof(y)=='string'?eval(y):y)+'">'+content+'</DIV>');   
    
  var   newItem   =   {};   
  newItem.object   =   document.getElementById(id);   
  newItem.x   =   x;   
  newItem.y   =   y;   
    
  this.items[this.items.length]   =   newItem;   
  }   
  this.play   =   function()   
  {   
  collection   =   this.items   
  setInterval('play()',10);   
  }   
  }   
  function   play()   
  {   
    
  for(var   i=0;i<collection.length;i++)   
  {   
  var   followObj   =   collection[i].object;   
  var   followObj_x   =   (typeof(collection[i].x)=='string'?eval(collection[i].x):collection[i].x);   
  var   followObj_y   =   (typeof(collection[i].y)=='string'?eval(collection[i].y):collection[i].y);   
    
//  if(followObj.offsetLeft!=(document.body.scrollLeft+followObj_x))   {   
  if(followObj.offsetLeft!=(document.documentElement.scrollLeft+followObj_x))   {   
//  var   dx=(document.body.scrollLeft+followObj_x-followObj.offsetLeft)*delta;   
  var   dx=(document.documentElement.scrollLeft+followObj_x-followObj.offsetLeft)*delta;   
  dx=(dx>0?1:-1)*Math.ceil(Math.abs(dx));   
  followObj.style.left=followObj.offsetLeft+dx;   
  }   
    
//  if(followObj.offsetTop!=(document.body.scrollTop+followObj_y))   {   
  if(followObj.offsetTop!=(document.documentElement.scrollTop+followObj_y))   {   
//  var   dy=(document.body.scrollTop+followObj_y-followObj.offsetTop)*delta;   
  var   dy=(document.documentElement.scrollTop+followObj_y-followObj.offsetTop)*delta;   
  dy=(dy>0?1:-1)*Math.ceil(Math.abs(dy));   
  followObj.style.top=followObj.offsetTop+dy;   
  }   
  followObj.style.display   =   '';   
  }   
  }     
    
  var   theFloaters   =   new   floaters();   
//  theFloaters.addItem('followDiv1','document.body.clientWidth-110',230,'<a   href=http://wpa.qq.com/msgrd?V=1&Uin=11111111&Menu=yes   target=_blank><img   src=images/4.gif   border=0></a><br><br>');   
  theFloaters.addItem('followDiv1','document.documentElement.clientWidth-110',230,'<a   href=http://wpa.qq.com/msgrd?V=1&Uin=11111111&Menu=yes   target=_blank><img   src=images/4.gif   border=0></a><br><br>');   
  theFloaters.play();   //-->
</script>
<div style="height:999px"></div>
</body></html>