$(function() {
  var move = function() {
    if (($(".slide_item").length-1) * -510 >= parseInt($("#slideshow_slides").css("margin-left"))) {
      $("#slideshow_slides").animate({"margin-left" : "0"});
    } else {
      $("#slideshow_slides").animate({"margin-left" : "-=510"});
    }
    setTimeout(move, 5000);
  };
  setTimeout(move, 5000);
});