怎么在一个单元格里定位一个层？

<body onload="init()">
<script>
function init(){
var dv=document.getElementById("v")
var t1=document.getElementById("td1")
dv.style.pixelTop=t1.offsetTop+t1.offsetParent.offsetTop
dv.style.pixelLeft=t1.offsetLeft+t1.offsetParent.offsetLeft+t1.offsetWidth
dv.style.pixelHeight=t1.offsetHeight
}
</script>
<table border="1" width="100">
  <tr>
    <td width="100%" id="td1">1</td>
  </tr>
  <tr>
    <td width="100%">2</td>
  </tr>
</table>
<div id=v style="position:absolute;background-color:#f2f2f2"><input type=button value=ok></div>
</body>