IE6下拉框图层问题探讨及解决

$("#div_bksq").bgiframe();

<script type="text/javascript" src="resources/js/plugins/jquery/jquery.bgiframe.min.js"></script>

<!-- 添加、申请以及修改布控页面开始 -->
<div class="gjcx_pop" style="display: none; background: white;height: 480px;margin-top:-240px;" id="div_bksq"><input type="text" style="display: none" id="txt_isViewOrUpdate"/>
<div class="gjcx_pop_tit" style="cursor: move;" id="div_bksq_tit">
<span><img src="resources/themes/default/images/vts/sourch_ico.gif" /><font class="sxcx_titText"><input type="text" id="txt_bt" style="border:0px;width:60px;font: normal bold 13px '宋体';color: #00517e;text-decoration: none;float:left;background: url('resources/themes/default/images/vts/alert_tit.jpg') repeat-x left top" /></font></span>
<img src="resources/themes/default/images/vts/alert_close.jpg" id="img_gb" style="cursor: pointer;" title="关闭"/>
</div>
<div class="qvyu" id="qyTree">
<div class="qvyu_n">