currentNavigationShown = "";

function slideNavigation(elementID)
{
  if (currentNavigationShown != elementID)
  {
    if (currentNavigationShown != "")
    {
      Effect.SlideUp(currentNavigationShown, {duration:1});      
    }
    currentNavigationShown = elementID;
    Effect.SlideDown(elementID, {duration:1});
  }
}