function onUdMouseDown(){
  var uddiv = document.getElementById('update');
  onMsgMove(uddiv);
}

function onMsgMove(divObj){
  var mx = event.clientX - parseInt(divObj.style.left);
  var my = event.clientY - parseInt(divObj.style.top);
  divObj.setCapture();
  divObj.onmousemove = mousemove; 
  divObj.onmouseup = mouseup;
  
  function mousemove(){
    var x = event.clientX;
    var y = event.clientY;
    divObj.style.left = x - mx;
    divObj.style.top = y - my;
  }
  
  function mouseup(){
    divObj.releaseCapture();
    divObj.onmousemove = function(){};
    divObj.mouseup = function(){};
  }
}