var popWindow; 

function open_NewWin(winURL, Width, Height) {    
  var Param;
  var lft=((screen.width - Width) / 2);
  var tp1=((screen.height - Height) / 2) - 20;  
  var tp2=((screen.height - Width) / 2) - 20;  
  var tp=20;
  if (tp1 < tp2) tp=tp1; 
  if (tp2 < tp1) tp=tp2; 
  Param = "left=" + lft +",top="+ tp +",width="+Width+",height="+Height+",menubar=no,toolbar=no,directories=no,scrollbars=no,resizable=yes,status=yes";
  popWindow = window.open(winURL,"Screen",Param);
}