Very easy way to preload images which are needed later (e.g. when a hover is performed) (from css-tricks.com !!!)

Image Preloader

$.preloadImages = function() {
  for (var i = 0; i < arguments.length; i++) {
    $("<img />").attr("src", arguments[i]);
  }
}

$.preloadImages("hoverimage1.jpg","hoverimage2.jpg");