<script>
if(typeof(HTMLElement)!="undefined")
HTMLElement.prototype.contains=function(obj)
{
  if(obj==this)return true;
  while(obj=obj.parentNode)if(obj==this)return true;
  return false;
} 
function doit(evt){
    evt = window.event || evt;
    var obj = evt.toElement || evt.relatedTarget;
    var pa = document.getElementById("pad");
    if(pa.contains(obj)) return false;
       alert('out');
}
</script>

<div id="pad" onmouseout="doit(event);" style="padding:10px;width:200px;height:200px;background:#CCC">
    <div style="background:#FFF">xxxxxx</div>
</div>