function setName(element,id,gesperrt) {

    // Request erzeugen
    if (window.XMLHttpRequest) {
       ...
        // Request auswerten
        request.onreadystatechange = interpretloadsetKonto;
    }
}

// Request auswerten
function interpretloadsetKonto() {
    switch (request.readyState) {
        ...
            } else {                
                if (request.responseText == "false")    {  
                    element.src='img/false.png';
                    element.width = 16;
                    element.height = 16;
                }else
                if (request.responseText == "true")    {  
                    element.src='img/true.png';
                    element.width = 16;
                    element.height = 16;
                }
                
            }
            break;
        default:
            break;
    }
}