$(document).ready(function(){

  var i=0;
  banners = new Array();
  $("#hot_news a.hot").each(function(){
    banners[i]=$(this).attr("num");
    i++;
  });

  if(i>1) changeBanner();

});

function changeBanner()
{

  $("#hot_news a.hot").hide();
  var size = $("#hot_news a.hot").length-1;
  var current = Math.floor(Math.random()*(size+1));
  $("#hot_news a.hot[num="+banners[current]+"]").show();
  setTimeout(changeBanner,5000);
}