$(window).load(function(){
    setInterval ( "slideSwitch(2000)", 3000 );
});

function slideSwitch(switchSpeed) {
    var $active = $('#slideshow img.active');
    if ( $active.length == 0 ) $active = $('#slideshow img:last');
    var $next =  $active.next('img').length ? $active.next('img') : $('#slideshow img:first');
    $active.addClass('last-active');
    $next.css({opacity: 0.0}).addClass('active').animate({opacity: 1.0}, switchSpeed, function() {
      $active.removeClass('active last-active');
    });
}