var url = 'messaggio.htm';
  wdt=window.screen.availWidth
  hdt=window.screen.availHeight
  if( (hdt < 480) || (wdt < 640) )
  {window.alert('sorry, you need a higher resolution to view this site'); }
  else
  function get_vcenter(wnd) {
  pos = (screen.availHeight - 350)/2;
  return(pos);
  }
  function get_hcenter(wnd) {
  pos = (screen.availWidth - 780)/2;
  return(pos);
  }