userAgent = window.navigator.userAgent;
browserVers = parseInt(userAgent.charAt(userAgent.indexOf("/")+1),10);
function newImage(arg) {
        if (document.images) {
                rslt = new Image();
                rslt.src = arg;
                return rslt;
        }
}

function findElement(n,ly) {
        if (browserVers < 4)                return document[n];
        var curDoc = ly ? ly.document : document;
        var elem = curDoc[n];
        if (!elem) {
                for (var i=0;i<curDoc.layers.length;i++) {
                        elem = findElement(n,curDoc.layers[i]);
                        if (elem) return elem;
                }
        }
        return elem;
}

function changeImages() {
        if (document.images && (preloadFlag == true)) {
                var img;
                for (var i=0; i<changeImages.arguments.length; i+=2) {
                        img = null;
                        if (document.layers) {
                                img = findElement(changeImages.arguments[i],0);
                        }
                        else {
                                img = document.images[changeImages.arguments[i]];
                        }
                        if (img) {
                                img.src = changeImages.arguments[i+1];
                        }
                }
        }
}

var preloadFlag = false;
function preloadImages() {
        if (document.images) {
                button_portfolio_over = newImage("bilder/button-portfolio-over.gif");
                button_referenzen_over = newImage("bilder/button-referenzen-over.gif");
                button_info_over = newImage("bilder/button-info-over.gif");
                button_kontakt_over = newImage("bilder/button-kontakt-over.gif");
                button_impressum_over = newImage("bilder/button-impressum-over.gif");
                preloadFlag = true;
        }
}