$(document).ready(function(){
  var banner = new Array();
  banner[0] = "<img src=\"images/slider1.jpg\" />";
  banner[1] = "<img src=\"images/slider2.jpg\" />";
  banner[2] = "<img src=\"images/slider3.jpg\" />";

  var randomBanner = Math.floor(Math.random()*banner.length);
  $('#slideshow').html(banner[randomBanner]);
});