function menu_mouse_events(button, event){
    ext = "png";
    if (document.all && !window.opera && !window.XMLHttpRequest) { ext = "gif" }
    if(event == "over")
        image = "img/buttonMouseOver." + ext;
    else if(event == "down")
        image = "img/buttonMouseDown." + ext;
    else
        image = "img/button." + ext;
    button.style.backgroundImage = 'url(/App_Themes/Default/' + image + ')';
}