.ConverDivCss 
    {
        width: 100%;
        height: 100%;
        left:0;
        top:0;/*FF IE7*/
        filter:alpha(opacity=50);/*IE*/
        opacity:0.5;/*FF*/
        z-index:100000;
        background-color:Black;
        position:fixed!important;/*FF IE7*/
        position:absolute;/*IE6*/

        _top:       expression(eval(document.compatMode &&
                    document.compatMode=='CSS1Compat') ?
                    documentElement.scrollTop + (document.documentElement.clientHeight-this.offsetHeight)/2 :/*IE6*/
                    document.body.scrollTop + (document.body.clientHeight - this.clientHeight)/2);/*IE5 IE5.5*/
    } 
     .mainfloatCSS {
left:45%;/*FF IE7*/
top:40%;/*FF IE7*/
z-index:100001;
margin-left:-150px!important;/*FF IE7 该值为本身宽的一半 */
margin-top:-60px!important;/*FF IE7 该值为本身高的一半*/

margin-top:0px;

position:fixed!important;/*FF IE7*/
position:absolute;/*IE6*/

_top:       expression(eval(document.compatMode &&
            document.compatMode=='CSS1Compat') ?
            documentElement.scrollTop + (document.documentElement.clientHeight-this.offsetHeight)/2 :/*IE6*/
            document.body.scrollTop + (document.body.clientHeight - this.clientHeight)/2);/*IE5 IE5.5*/

}