var tab_zakladki = new Array('zakladka1', 'zakladka2','zakladka3','zakladka4');

function zakladki_najnowsze(id_zakladki, nr){
  
    for(i=0; i<tab_zakladki.length; i++ ){
       document.getElementById(tab_zakladki[i]).style.display = 'none';
       document.getElementById('zak'+ (i+1)).className='zak'+(i+1)+'_off';
    }    
    document.getElementById(id_zakladki).style.display="block";
    document.getElementById('zak'+ nr).className='zak'+nr+'_on';       
}