解决IE6下select显示在弹出框上问题

利用定位position:absolute;z-index:1;和iframe[z-index:-1]来解决此问题，最好根据需要加上： border='0' frameborder='0' scrolling='no'来去除滚动条和边框，需要使用jquery1.7.2.js。

解决方法：

1.将iframe放到弹出层的最外层里的最后面，也可以是里面，定义z-index:-1;。

<div  class="left_main_menu">
       <div class="left_menu_left">
           <asp:Literal ID="Literal1" runat="server"></asp:Literal>
       </div>
       <div class="left_menu_right" title="点击隐藏菜单">
          <div class="left_menu_rightbody">隐藏菜单</div>
          <iframe style="position: absolute; left: -800px; top: -600px; z-index: -1;  2048px; height: 1800px; *position: absolute; opacity: 0.3; filter: alpha(opacity=10);"></iframe>
        </div>
   </div>

css

<style type="text/css">
.left_main_menu{180px;height:auto;position:fixed;left:0;top:40px;border:1px solid #ccc;box-shadow:0px 0px 30px rgb(170,170,170);padding:2px;background-color:#0099CC;overflow:hidden;z-index:999;-moz-border-radius:5px;-webkit-border-radius:5px;border-radius:5px;_position:absolute;}
.left_main_menu .left_menu_left{163px;height:100%;overflow:auto;overflow-x:hidden;float:left;background:#F5FAF1;}
.left_main_menu .left_menu_right{15px;height:100%;float:right;background:#0099cc;text-align:center;cursor:pointer;color:#FFFFFF;font-weight:bold;}
.left_main_menu .left_menu_right:hover{background:#F5FAF1;color:#0099CC;}
.left_main_top a,.left_main_se a{height:28px;100%;text-align:center;line-height:28px; display:inline-block; color:#0099CC; cursor:pointer; text-decoration:none;_padding-top:8px; }
.left_main_top a{font-size:14px;font-weight:bold;background:#F0F0F0; border-top:1px solid #0099CC; border-bottom:1px solid #0099CC;}
.left_main_se a{ font-size:12px; font-weight:lighter;background:#F5FAF1;border-top:1px solid #0099CC;}
.left_main_top a:hover,.left_main_topcurrent a{background:#D0D0D0;cursor:pointer;height:28px;100%;text-align:center;line-height:28px; display:inline-block;text-decoration:none;}
.left_main_se a:hover,.left_main_securrent a{background:#D0D0D0;cursor:pointer;height:28px;100%;text-align:center;line-height:28px; display:inline-block;text-decoration:none;}
.left_main_lcon{height:24px;24px;vertical-align:middle;line-height:24px;}
.left_main_menu ul{margin:0px;padding:0px;}
</style>

2.在需要的层后面增加一个层来隐藏select，建议样式选择一样，设置z-index:999，弹出层:z-index:1000。

<div class="global-topwhs" id="topcss" style="z-index:1000">
    <div class="glo-m">
        <div class="glo-left">
            <div class="glo-left-font">
                 <label>信息化系统欢迎您</label>
            </div>

        </div>
        <div class="glo-right">
             <label class='glo-tui'><a href="javascript:void(0)" id="signoutsystem">退出</a></label>
        </div>
    </div>
</div>
<div class="global-topwhs"  style="z-index:999">
<iframe style="position: absolute; left: -800px; top: -600px; z-index: -1;  2048px; height: 1800px; *position: absolute; opacity: 0.3; filter: alpha(opacity=10);"></iframe>
</div>

3.第二种方式的整合体，iframe这里只对ie6有隐藏的目的，所以应该对于ie6生成，其它浏览器不生成ifram.js，哪里要用放到哪里。

//说明：
/****************************************************************************/
/**引用此文件的位置ie6下后面追加一个iframe,需要定义iframe的高宽左上四个参数**/
/****************************************************************************/
$(function () {
    if ($.browser.msie && parseInt($.browser.version) <= 6) {
        //是ie6，写iframe
        $("script").each(function () {
            if ($(this).attr('src') == '/js/ifram.js' && !$(this).next().is("iframe[tag=ie6]")) {
                var height = $(this).attr('h');
                var width = $(this).attr('w');
                var left = $(this).attr('l');
                var top = $(this).attr('t');
                var tt = $(this).attr('tt');
                if (tt == 'tt') {
                    $(this).after("<div tag=ie6 class='global-topwhs' style='z-index:999;background:red;'><iframe border='0' frameborder='0' scrolling='no' style='position: absolute; left:" + left + "; top: " + top + "; z-index: -1;  " + width + "; height: " + height + "; *position: absolute; opacity: 0.3; filter: alpha(opacity=10);'></iframe></div>");
                } else {
                    $(this).after("<iframe tag=ie6 border='0' frameborder='0' scrolling='no' style='position: absolute; left:" + left + "; top: " + top + "; z-index: -1;  " + width + "; height: " + height + "; *position: absolute; opacity: 0.3; filter: alpha(opacity=10);'></iframe>");
                }
            }
        });
    }
});