var rotate = {
    loaded: [],
    current: 0,

    init: function() {
        if (!logos.length) return false;
        if (!$("logo")) return false;
        for (var i=0; i < logos.length; i++) {
            var img = new Image();
            var fn = rotate.image_loaded.bind(rotate, logos[i]);
            Event.observe(img, 'load', fn); 
            img.src = logos[i];
        }
        new PeriodicalExecuter(rotate.next, 3);
    },

    image_loaded: function(src) {
        rotate.loaded.push(src);
    },

    next: function() {
        if (rotate.current > rotate.loaded.length-1) rotate.current = 0;
        $("logo").style.backgroundImage = "url(" + rotate.loaded[rotate.current] + ")";
        return rotate.current++;
    }
}

Event.observe(window, 'load', rotate.init.bindAsEventListener(rotate));