在ie和firefox上为什么显示不同?如何解决,谢谢!!

#holder_default

{

    margin: 4px auto 4px auto;

    width: 742px;

}

#foot

{

    border-width: 1px 1px 1px 1px;

    border-style: solid;

    border-color: #C0C0C0;

    width: 740px;

    background-color: #E4E4E4;

    margin-right: auto;

    margin-left: auto;

    color: #A7A4A4;

}

#part_left

{

    float: left;

    width: 240px;

    display: inline;

    margin-right: 4px;

    margin-bottom: 4px;

}

#part_right

{

    display: inline;

    float: left;

    width: 498px;

}

        <div id="holder_default">

            <div id="part_left">

                <div class="box" id="news_box">

                    <div class="title">

                        News</div>

                    <p>

                        we have goog news.</p>

                </div>

                <div class="box" id="card_box">

                    <div class="title">

                        Card</div>

                    <p>

                        this is card.</p>

                </div>

            </div>

            <div id="part_right">

                <div class="box">

                    <div class="title">

                        Products</div>

                    <p>

                        Products.</p>

                </div>

            </div>

        </div>

        <div id="foot">

            <p>

                Copyright © 2008, All Rights Reserved</p>

        </div>

为什么在ie中显示的是foot在holder_default下方,而在firefox中显示的foot与holder_default平齐显示,以至于在firefox中实际现实的foot在Pert_left和part_right的底层显示,我要的是ie中的效果,谢谢大家了,正学习CSS中...