zl_slide_pos = 1;

function zl_slideshow() {
  new Effect.Fade("zl-slideshow-"+zl_slide_pos, { duration:1, from:1.0, to:0.0 });
  zl_slide_pos++;
  if (zl_slide_pos > 4) zl_slide_pos = 1;
  new Effect.Appear("zl-slideshow-"+zl_slide_pos, { duration:1, from:0.0, to:1.0 });
	setTimeout(zl_slideshow, 4000);
}

Event.observe(window, 'load', function () {
	setTimeout(zl_slideshow, 4000);
});