var popupWindow=null;

function popup (mypage, myname, w, h, pos, infocus)
{

   if (pos == 'random')
   {
      LeftPosition = (screen.width) ? Math.floor (Math.random () * (screen.width - w)) : 100;
      TopPosition = (screen.height) ? Math.floor (Math.random () * ((screen.height - h) - 75)) : 100;
   }
   else
   {
      LeftPosition = (screen.width) ? (screen.width-w) / 2 : 100;
      TopPosition = (screen.height) ? (screen.height - h) / 2 : 100;
   }

   settings = 'width=' + w + ',height=' + h + ',top=' + TopPosition + ',left=' + LeftPosition + ',scrollbars=no,location=no,directories=no,status=no,menubar=no,toolbar=no,resizable=no';
   popupWindow = window.open ('', myname, settings);

   if (infocus=='front')
   {
      popupWindow.focus();
      popupWindow.location=mypage;
   }

   if(infocus=='back')
   {
      popupWindow.blur();
      popupWindow.location=mypage;
      popupWindow.blur();
   }
}