function PreLoadImages(){
    var leftBgHover, rightBgHover, menuBgHover;
    leftBgHover = new Image();
    rightBgHover = new Image();
    menuBgHover = new Image();
    leftBgHover.src = '/images/menu_buttons/menu_left_bg_hover.jpg';
    rightBgHover.src = '/images/menu_buttons/menu_right_bg_hover.jpg';
    menuBgHover.src = '/images/menu_buttons/menu_bg_hover.jpg';
}

function NavBarHover(tdToChange,direction){
  if(direction!=null){
    document.getElementById('tdNav'+direction).style.backgroundImage="url('/images/menu_buttons/menu_"+direction+"_bg_hover.jpg')";
    }
  tdToChange.style.backgroundImage="url('/images/menu_buttons/menu_bg_hover.jpg')";
  }
function NavBarNormal(tdToChange,direction){
  if(direction!=null){
    document.getElementById('tdNav'+direction).style.backgroundImage="url('/images/menu_buttons/menu_"+direction+"_bg.jpg')";
    }
  tdToChange.style.backgroundImage="url('/images/menu_buttons/menu_bg.jpg')";
}