function slideSwitch() {
  var $active = jQuery('#slideshow_box img.active');
  
  if ( $active.length == 0 ) $active = jQuery('#slideshow_box img:last');

  var $next =  $active.next().length ? $active.next()
    : jQuery('#slideshow_box img:first');

  $active.addClass('last-active');

  $next.css({opacity: 0.0})
    .addClass('active')
    .animate({opacity: 1.0}, 1000, function() {
      $active.removeClass('active last-active');
    });
}

jQuery(function() {
  setInterval("slideSwitch()", 6000);
});