var akt_bild = 'null';

  if (document.images){
   m1a = new Image(); m1a.src="images/login01a.gif";
   m1b = new Image(); m1b.src="images/login02c.gif";
   m2a = new Image(); m2a.src="images/login01b.gif";
   m2b = new Image(); m2b.src="images/login02c.gif";
   m3a = new Image(); m3a.src="images/veranstaltungen01a.gif";
   m3b = new Image(); m3b.src="images/veranstaltungen01b.gif";
   m4a = new Image(); m4a.src="images/publikationen01a.gif";
   m4b = new Image(); m4b.src="images/publikationen01b.gif";
  }

  function Change(nr_bild,id_button){
   if (document.images){
    if (nr_bild != akt_bild){  
     document.images[nr_bild].src = eval(id_button + ".src");
    }
   }
  }