function Menu() {
  var Obj = this;
  var DOMAIN = "http://www.diablock.co.jp/";
  var DIR = DOMAIN + "_common/_img/";
  var current = "";
  var ids = {
    home  : 2,
    about : 3,
    catalog : 4,
    fan  : 5,
    happy  : 6,
    press  : 7
  };
  Obj.swapOver = function(_img, _num) {
     _img.src = DIR + "navi" + _num + ".gif";
  }
  
  Obj.swapOut = function(_img, _num) {
    if (ids[current] != _num) {
      _img.src = DIR + "navi0" + _num + ".gif";
    }
  }
  
  Obj.highlight = function(_id) {
    var m = document.getElementById("nav-" + _id);
    if (m) m.src = DIR + "navi" + ids[_id] + ".gif";
    current = _id;
  }
}

var nv = new Menu();