var banners = new Array('<div class="top_banner_2007"></div>', '<div class="top_banner_2008"></div>', '<div class="top_banner_2009"></div>', '<div class="top_banner_2010"></div>', '<div class="top_banner_the_balance_of_guilt"></div>');
var max = banners.length;
var num = Math.floor((Math.random() * max));