function submenu(sm){
    var s=document.getElementById('submenu'+sm);
    var m=document.getElementById('mainitem'+sm);
    if(s.style.display!='block'){
        s.style.display='block';
        m.style.background='url(\'/images/menu_minus.gif\') 5px 5px no-repeat';
    } else {
        s.style.display='none';
        m.style.background='url(\'/images/menu_plus.gif\') 5px 5px no-repeat';
    }

}