function doSlideShow(){ 
    var ajax = null;
    try{
        ajax = new XMLHttpRequest();
    }catch(e){
        try{
           ajax = new ActiveXObject('Microsoft.XMLHTTP');
        }catch(e){
            try{
                ajax = new ActiveXObject('Msxml2.XMLHTTP');
            }catch(e){
            holder.innerHTML = 'keine Ajax unterstützung';
            }
        }
    }
    
    ajax.onreadystatechange = function(){
        if(ajax.readyState == 4){
             document.getElementById("ads").innerHTML = ajax.responseText;
        }
    }
    
    ajax.open('GET', '/_ajax/slideshow.php?' + Math.round(Math.random() * 100), true);
    ajax.send(null);
    window.setTimeout('doSlideShow()', 4000);
    //return true;    
}
document.onload = doSlideShow();