var images = new Array();

function changeBG(classname) {
    document.getElementById('main').className = classname;
}

function preloadImages() {
    for (i = 0; i < preloadImages.arguments.length; i++) {
        images[i] = new Image();
        images[i].src = preloadImages.arguments[i];
    }
}

preloadImages("images/accueil.jpg", "images/art.jpg", "images/expos.jpg", "images/galerie.jpg", "images/contact.jpg");