模拟frameset问题

<SCRIPT>
var ms=0;
var width=0;
function did(obj){
          ms=obj;
          width=document.getElementById("runbar").clientWidth-2;
          document.all(ms).setCapture();
          x=document.all(ms).style.pixelLeft-event.clientX;
}
function document.onmousemove(){
          if(ms){
           var tempWidth=width+x+event.clientX;
           if(tempWidth<0) tempWidth=0;//防止左移得太多
           if(tempWidth>750) tempWidth=750;//防止右移太多
            document.getElementById("runbar").style.width=tempWidth;
          }
    
}
function document.onmouseup(){
         if(ms){
          document.all(ms).releaseCapture();
     ms=0;
         }
}
</SCRIPT><head>
</HEAD>
<BODY>
<input   id=x1 ><input   id=y1 >
<br/>             
<center>
<TABLE id="tb" border=10 width=800 height=200px cellpadding=0  cellspacing=0 style="table-layout:fixed;">
<tr><td id=runbar width=100>
<div style="width:100%;height:100%;overflow:auto"><table width=100% height=100% border=0 ><tr><td>xxxxxxxxxx</td></tr></div></table></div>
</td>
<td width=20>
<DIV onmousedown="did('a1')"
  id=a1 style="POSITION:relative;border: 1px solid #ffaa12;WIDTH: 
20; HEIGHT: 100%;cursor: e-resize">拖动层
</DIV></td>
<td><iframe style="width:100%;height:100%" src=""></iframe></td></tr></Table>
</center></BODY>