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

$(function() {
  var bkg_imgs = ["/public/images/header1.jpg",
                  "/public/images/header2.jpg",                  
                  "/public/images/header3.jpg",                                    
                  "/public/images/header4.jpg"];
  $.preloadImages(bkg_imgs);
  var randomnummber = Math.floor(Math.random()*4 ),
      url = "url(" + bkg_imgs[randomnummber] + ")";
  if($("body").attr("id") === "hmpg") {
    $("div.container").css("background", "transparent url(/public/images/header1.jpg) no-repeat scroll center top");    
  } else {
    $("div.container").css("background", "transparent " + url + " no-repeat scroll center top");          
  }
});