function showSubMenu(menuitem)
{
    d = document;
    submenudiv  = d.getElementById('menu-sub');
    submenus = submenudiv.getElementsByTagName('div');
    for (var i = 0; i < submenus.length; i++)
    {
        submenu = submenus[i];
        submenuname = submenu.attributes.getNamedItem('id').nodeValue;
        if(submenuname == menuitem)
        {
            submenu.style.display = '';
        }
        else
        {
            submenu.style.display = 'none';
        }
    }
}