var iTotal = 4;

    function showNav(navID)
    {
        hideNav();
        document.getElementById("subNav" + navID).style.visibility = "visible";
    }

    function hideNav()
    {
        for(i=1; i<=iTotal; i++)
        {
            document.getElementById("subNav" + i).style.visibility = "hidden";
        }
    }