current_menu = null;
timer_fn     = 0;
menu_timeout = 250;

function show_sub_menu(id) {
    cancel_timeout();
    if(current_menu) {
        document.getElementById(current_menu).style.display='none';
    }

    if(id) {
        document.getElementById(id).style.display='inline';
    }

    current_menu = id;
}

function timeout_event() {
    timer_fn = window.setTimeout('show_sub_menu(0)', menu_timeout);
}

function cancel_timeout() {
    if(timer_fn) {
        window.clearTimeout(timer_fn);
        timer_fn = null;
    }
}