var count = 4; 
    var imagePreload = new Array(count);
    var i = Math.round(Math.random()*count);

    function slideshow(){
    var path = new Array("/images/header/");
    var filetype = "jpg";

     if (imagePreload[i] == null){
        imagePreload[i]     = new Image();
        imagePreload[i].src = path + i + "." + filetype;
        //alert("Lade vom Server Bild " + i);
    }//end if null
       document.images[1].src = imagePreload[i].src;  
    
    setTimeout('slideshow()',30000);
    if (i<count){
        i++;}
    else{
        i = 0;
    }   
 }