// Basic

function layer(layerName){

  if(document.getElementById) return document.getElementById(layerName) // DOM1 
  if(document.all) return document.all[layerName] // MSIE4
  if(document.layers) return document.layers[layerName] // Netscape 4
  return null // unsupported browser
}

// Images

var mainMenuBG = new Image();

function preloadImg(url){

    Img = new Image();
    Img.src = url;

	return Img;
}

function changeMainMenuBG(menuItem){

	menuItem.style.backgroundImage = "url(" + mainMenuBG.src + ")";
}

function defaultMainMenuBG(menuItem){

	menuItem.style.backgroundImage = "";
}

mainMenuBG = preloadImg("images/mainmenu_bg_hover.png");