function newImage(arg) {
                if (document.images) {
                        rslt = new Image();
                        rslt.src = arg;
                        return rslt;
                }
        }
        
        function changeImages() {
                if (document.images && (preloadFlag == true)) {
                        for (var i=0; i<changeImages.arguments.length; i+=2) {
                                document[changeImages.arguments[i]].src = changeImages.arguments[i+1];
                        }
                }
        }
        
        var preloadFlag = false;
        function preloadImages() {
                if (document.images) {
                        header_button_1_over = newImage("images/header_button_1_over.gif");
                        header_button_2_over = newImage("images/header_button_2_over.gif");
                        header_button_3_over = newImage("images/header_button_3_over.gif");
                        header_button_4_over = newImage("images/header_button_4_over.gif");
                        header_button_5_over = newImage("images/header_button_5_over.gif");
                        preloadFlag = true;
                }
        }