var pp_open=false,  pp_window=null;

function checkWindow()
{   if ( pp_open )
    { if ( pp_window == null ) pp_window=window.open('',"paypal");
      if ( pp_window.closed ) {  pp_window=null;  return true; }
      pp_window.focus();
    }
    pp_open=true;
    return true;
}