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) {
        main_or_over = newImage("images/main-or_over.gif");
        main_yl_over = newImage("images/main-yl_over.gif");
        main_tq_over = newImage("images/main-tq_over.gif");
        main_pr_over = newImage("images/main-pr_over.gif");
        main_gr_over = newImage("images/main-gr_over.gif");
        main_bl_over = newImage("images/main-bl_over.gif");
        main_pk_over = newImage("images/main-pk_over.gif");
        preloadFlag = true;
    }
}