function overNav()
{
  if (document.getElementById('submenu').className == 'submenu_hidden')
  {
    document.getElementById('submenu').className = 'submenu';
  }
}

function outNav()
{
  if (document.getElementById('submenu').className == 'submenu')
  {
    document.getElementById('submenu').className = 'submenu_hidden';
  }
}