<body onscroll="f()">
<script>
var x,y
function window.onload(){
with(document.all.a.style){
x=left;y=top;
}
}
function f(){
with(document.all.a.style){
pixelLeft=document.body.scrollLeft
pixelTop=document.body.scrollTop
}
}
</script>
<div id=a style="position:absolute;top:0;left:0;z-index:2;background-color:red">fason</div>
</body>
<script>
var x,y
function window.onload(){
with(document.all.a.style){
x=left;y=top;
}
}
function f(){
with(document.all.a.style){
pixelLeft=document.body.scrollLeft
pixelTop=document.body.scrollTop
}
}
</script>
<div id=a style="position:absolute;top:0;left:0;z-index:2;background-color:red">fason</div>
</body>
<div id="demo" style="position:absolute;z-index:2;overflow:auto;height:80px;width:500" >
<table border="1" style="position:absolute;z-index:2;" bgcolor=#ff00ff width=100% id=t0>
<tr>
<td id="td1">ttt</td>
<td>ttt中国人</td>
<td>ttt</td>
</tr>
</table>
</div></body>
http://www.ccidnet.com/school/web/2002/06/17/100_6712.html
我稍微做了一下修改，就搞定了。没有什么难度：
<SCRIPT FOR=window EVENT=onload LANGUAGE="JavaScript">
initAd();//载入页面后，调用函数initAd()
</SCRIPT>
<script language="JavaScript">
<!--
function initAd() {
document.all.AdLayer.style.posTop = -200;
//设置onLoad事件激发以后，广告层相对于固定后的y方向位置
document.all.AdLayer.style.visibility = 'visible'//设置层为可见
MoveLayer('AdLayer');//调用函数MoveLayer()
}
function MoveLayer(layerName) {
var x = 600;//浮动广告层固定于浏览器的x方向位置
var y = 300;//浮动广告层固定于浏览器的y方向位置
var diffy = (document.body.scrollTop + y - document.all.AdLayer.style.posTop)*.40;
var y = document.body.scrollTop + y - diffy;
var diffx = (document.body.scrollLeft + x - document.all.AdLayer.style.posLeft)*.40;
var x = document.body.scrollLeft + x - diffx;
eval("document.all." + layerName + ".style.posTop = y");
eval("document.all." + layerName + ".style.posLeft = x");//移动广告层
setTimeout("MoveLayer('AdLayer');", 20);//设置20毫秒后再调用函数MoveLayer()
}
//-->
</script>
<!--下面为一个ID为AdLayer的层(如ID名不为AdLayer，
上面MoveLayer()内的AdLayer也要作相应修改)，包括一张带链接的图片-->
<div id=AdLayer style='position:absolute; width:61px; height:59px; z-index:20; visibility:hidden;; left: 600px; top: 300px'>
<a href="http://www.5dmedia.com/bbs"><img src='../qqkk2000.gif' border="0" height="60" width="60"></a>
</div>
var diffy = (document.body.scrollTop + y - document.all.AdLayer.style.posTop)*.40;
var y = document.body.scrollTop + y - diffy;
var diffx = (document.body.scrollLeft + x - document.all.AdLayer.style.posLeft)*.40;
具体的含义，你自己慢慢体会吧！
阿信和司令的代码更简单，更好。推荐！
<script>
var x,y
function window.onload(){
with(document.all.a.style){
x=left=100
y=top=100
}
}
function f(){
with(document.all.a.style){
pixelLeft=x+document.body.scrollLeft
pixelTop=y+document.body.scrollTop
}
}
</script>
<div id=a style="position:absolute;background-color:red">fason</div>
</body>