//open pop-up window
function popup (winName, url)
{
  var popWidth = 590, popHeight = 500, scrolling = true;
  
  if (scrolling === true) scrolling = 'yes';
  
  var leftPos = (screen.availWidth - popWidth) / 2;
  var rightPos = (screen.availHeight - popHeight) / 2;
  
  var details = "height=" + popHeight + ",width=" + popWidth + ",left=" + leftPos + ",top=" + rightPos + ",status=no,resizable=yes,titlebar=no,toolbar=no,location=no,scrollbars=yes,directories=no";
  
  if (winName && winName.open && !winName.closed){
    winName.resizeTo(popWidth, popHeight);				//only works in IE
    winName.location = url;
    winName.focus();
  }
  else { 
    winName = window.open(url, winName, details);
    winName.focus();
  }
  return false;
}