Add a reference to jquery.js and the jquery css file in your view/_layout and for the textbox:

@Html.TextBox(x => x.Something, new { @class = "date" })

EDIT: Forgot about the little snippet of JS needed to make this work

    <script>
        $(document).ready(function () {
            $('.date').datepicker({ dateFormat: "mm/dd/yy" });
        });
    </script>