[jQuery] Need help with animations in IE

[The Sixth Halcon]

Hi, this is one of my firsts experiences with jQuery and I have a
little problems already.
The problem explanation is that I want to apply an effect to a css
layer (and it is applied) that when you click on a special div, it
moves some layers. It works perfectly with Firefox, but not in IE...
I leave here the css code and the jQuery script...

//////////////////////////////  jQuery
<script type="text/javascript">
  $(document).ready(function(){
        var selected_opt = 0;
        var speed        = 300;

        $("#contentbox4").animate({
          opacity: 0
    });


    $("#footer_lt").click(function () {
          $("#contentbox1").animate({
        opacity: 0,
        left: "-500px"
      }, speed );
          $("#contentbox2").animate({
        left: "0px"
      }, speed );
          $("#contentbox3").animate({
        left: "311px",
      }, speed );
          $("#contentbox4").animate({
            opacity: 100,
        right: "0px"
      }, speed );

          selected_opt = 1;
    });


        $("#footer_rt").click(function () {
          $("#contentbox1").animate({
        opacity: 100,
        left: "0px"
      }, speed );
          $("#contentbox2").animate({
        left: "311px"
      }, speed );
          $("#contentbox3").animate({
                left: "622px"
      }, speed );
          $("#contentbox4").animate({
            opacity: 0,
        right: "-500px"
      }, speed );
    });

  });
</script>

//////////////////////////////  CSS
#contentbox1 {
        position:absolute;
        left:0px;
        top:80px;
        width:278px;
        height:439px;
}

#contentbox2 {
        position:absolute;
        left: 311px; /* 336px; <= Para el master950px */
        top:80px;
        width:278px;
        height:439px;
}

#contentbox3 {
        position:absolute;
        right:0px;
        top:80px;
        width:278px;
        height:439px;
}

#contentbox4 {
        position:absolute;
        right:-500px;
        top:80px;
        width:278px;
        height:439px;
}



You dont have to rewrite the code if you don't want (I don't want to
annoy anyone) but if you can explain me the error... ^^

Thanks anyway!