移动表单的问题

看看这个
<html>
<head>
<title> New Document </title>
<script language="JavaScript">
<!--
var sstr = "",moveable = false,x0=0,y0=0,x1=0,y1=0;
function startDrag()
{
        var offx=2,offy=2;
if(event.button==1)
        {
                var obj = document.all.Layer1;
obj.setCapture();
                //定义对象; 
                //记录鼠标和层位置;
x0=event.clientX;
y0=event.clientY;
                x1 = parseInt(obj.style.left);
                y1 = parseInt(obj.style.top);
                obj.style.left = x1 - offx;
                obj.style.top  = y1 - offy;
                moveable = true;
        }
}
function drag()
{
        if(moveable)
        {
                var obj = document.all.Layer1;
obj.style.left = x1 + event.clientX - x0;
                obj.style.top  = y1 + event.clientY - y0;
        }
}
function stopDrag()
{
        var offx=2,offy=2;
if(moveable)
        {
                
var obj = document.all.Layer1;
x1 = parseInt(obj.style.left);
                y1 = parseInt(obj.style.top);
obj.style.left = x1 + offx;
                obj.style.top  = y1 + offy;
                obj.releaseCapture();
moveable = false;
        }alert(obj.style.left+"         "+obj.style.top)
}
//-->
</script>
</head><body bgcolor="#FFFFFF">
<div onmousedown='startDrag()' onmouseup='stopDrag()' onmousemove='drag()' id='Layer1' style='position:absolute; display:; cursor:hand; left:300px; top:195px; width:200px; height:200px; z-index:1'><img id='imgtu' src='http://expert.csdn.net/images/csdn.gif'></div>
</body>
</html>