function InitNav () {
    if (document.getElementById) {
      i=0;
      while (obj = document.getElementsByTagName("div")[i]){
        if (obj.id.substr(0,3) == "nav") {
          obj.style.display = "none";
        }
        i++;
      }
    }
}

function showNav(id) {
  if (document.getElementById) {
    if (document.getElementById("nav"+id).style.display == "") {
      document.getElementById("nav"+id).style.display = "none";
    }
    else {
      document.getElementById("nav"+id).style.display = "";
    }
  }
}