function zakladka(id) {
    var div_id = new Array("zakladka-niusy", "zakladka-serwy", "zakladka-arty", "zakladka-komenty");
    for (var l=0; l<4; l++) {
        document.getElementById(div_id[l]).style.display = "none";
        document.getElementById(div_id[l]+"-menu").className = "nieaktywna";
    }
    document.getElementById(id).style.display = "block";
    document.getElementById(id+"-menu").className = "aktywna";
    return false;
}