Problem with tabbed script in IE8

Problem with tabbed script in IE8

Hi!
I'm trying to implement this script:
into my portfolio.

And after all customizing I realize that this one doesn't work in IE8 correctly.
In FF, Opera, Safari, Chrome, IE7 everything works excellent but only in the newest IE is problem.

Here's jQuery code which I use in my portfolio:
  1. var TabbedContent = {
    init: function() {
    $(".tab_item").mouseover(function() {

    var background = $(this).parent().find(".moving_bg");

    $(background).stop().animate({
    left: $(this).position()['left']
    }, {
    duration: 300
    });

    TabbedContent.slideContent($(this));

    });
    },

    slideContent: function(obj) {

    var margin = $(obj).parent().parent().find(".slide_content").width();
    margin = margin * ($(obj).prevAll().size() - 1);
    margin = margin * -1;

    $(obj).parent().parent().find(".tabslider").stop().animate({
    marginLeft: margin + "px"
    }, {
    duration: 300
    });
    }
    }

    $(document).ready(function() {
    TabbedContent.init();
    });

































Have you got any idea what should I do to fix this problem in IE8?