ie8以前版本，下拉框遮盖其他div问题

HiddenSelect(x_top, y_top, width, height)
传入当前层的右上角坐标和层的宽和高，即可以解决此问题。
以下是客户端的JavaScript代码：
function ShowWinLayer(width, height, layer){

    /* show window page */

    /* width: DIV显示的宽 */
   /* height: DIV显示的高 */
    /* layer: 在层上显示的内容 */

    var div = document.getElementById('divWinLayer');
    var clientWidth = document.body.clientWidth;
    var clientHeight = document.body.clientHeight;
    var scrollTop = document.body.scrollTop;
    var left = (clientWidth - width)/2;
    var top = (clientHeight - height)/2 * 0.8 + scrollTop;
    div.style.width = width;
    div.style.height = height;
    div.style.left = left;
    div.style.top = top;
    div.style.visibility = 'visible';
    //hidden select elements
    HiddenSelect(left, top, width, height);
    //bind innerHTML
    div.innerHTML = layer;
}

//hidden select elements function

function HiddenSelect(x_top, y_top, width, height){
var x_bt = x_top + width;
    var y_bt = y_top + height;
    var sl_pos,sl_x_top, sl_y_top, sl_x_bt, sl_y_bt, dsrcid;
    var sls = document.getElementsByTagName('SELECT');
    for(i=0; i<sls.length; i++){

       sl_pos = AbsPos(sls[i]);
       sl_x_top = sl_pos.x;
       sl_y_top = sl_pos.y;
       sl_x_bt = sl_x_top + sls[i].clientWidth;
       sl_y_bt = sl_y_top + sls[i].clientHeight;

             if(((sl_x_bt > x_top) && (sl_x_top < x_bt)) && ((sl_y_bt > y_top) && (sl_y_top < y_bt))){

           dsrcid = sls[i].parentNode;

           if(dsrcid){
              if(dsrcid.id.indexOf('nohidden') == -1){
                 sls[i].style.visibility = 'hidden';

               }

           }else{

               sls[i].style.visibility = 'hidden';

           }

       }else{

           sls[i].style.visibility = 'visible';

       }

    }
}