求助：下拉列表 ie6显示正常 ie8显示完全

ie6正常显示  ie8下拉列表超过表格的部分显示不出来  应该怎么修改啊 
或者最好有ie6 和ie8通用的方式
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部分代码如下:
<table width="100%" border="0" cellpadding="0" cellspacing="0"
style="overflow:hidden;position:relative;z-index:999;">
  <tr>
    <td width="10" height="8" background="images/search_bar_left_1.gif"></td>
    <td height="8" colspan="2" background="images/search_bar_content_1.gif"></td>
    <td width="10" height="8" background="images/search_bar_right_1.gif"></td>
  </tr>
  <tr>
    <td width="10" rowspan="3" background="images/search_bar_left_2.gif"></td>
    <td background="images/search_bar_content_2.gif"><h2>正在上机用户列表</h2></td>
    <td width="73" height="74" rowspan="3" background="images/search_bar_content_2_09.gif">
<input type="submit" value="查询" class="submit_button"
onclick="checkSearchIf()"/>
</td>
    <td width="10" rowspan="3" background="images/search_bar_right_2.gif"></td>
  </tr>
  <tr>
    <td background="images/search_bar_content_2.gif">
 
    </td>
  </tr>
  <tr><tr>
    <td background="images/search_bar_content_2.gif">
     <span class="fl span_style">过滤条件</span>
                    <div class="wbID_box fl">
                        <div id="search_if" class="wbID fl"
onclick="show_select_list('sub_search_if','sub_search_if','search_if','a','fileter')"></div>
<input name="fileter" id="fileter" type="text" class="dn" value=""/>
                        <ul id="sub_search_if" class="sub_wbID" style="display:none;">
                            <li><a href="#">卡号</a></li>
                            <li><a href="#">卡类型</a></li>
                            <li><a href="#">计费方式</a></li>
<li><a href="#">区域</a></li>
<li><a href="#">电脑</a></li>
<li><a href="#">IP</a></li>
                        </ul>
                    </div>
                    <input name="filtertext" type="text" id="filtertext" class="input_text fl" value="" />
                    <span class="fl span_style">排序</span>
                    <div class="wbID_box fl" id="sort_box">
                        <div id="sort" class="wbID fl" onclick="show_select_list('sub_sort','sub_sort','sort','a','order')">
</div>
<input name="order" id="order" type="text" value="" class="dn"/>
                        <ul id="sub_sort" class="sub_wbID" style="display:none;">
                            <li><a href="#">开始时间</a></li>
                            <li><a href="#">卡上余额</a></li>
                            <li><a href="#">剩余可用时间</a></li>
                            <li><a href="#">卡号</a></li>
                        </ul>
                    </div>
                    <div class="wbID_box fl" id="sort_t_box">
                    <div id="sort_t" class="wbID fl"
onclick="show_select_list('sub_sort_t','sub_sort_t','sort_t','a','orderby')"></div>
<input name="orderby" id="orderby" type="text" value="" class="dn"/>
                        <ul id="sub_sort_t" class="sub_wbID" style="display:none;">
                            <li><a href="#">降序</a></li>
                            <li><a href="#">升序</a></li>
                        </ul>
                    </div>
                    <div class="fl">
                        <input type="submit" class="btn" style="display:none" name="Submit2" value="上一页"/>
                        <input name="Page" class="input" style="display:none" type="text" id="Page" value="1"
size="2" />
                        <input type="submit" class="btn" style="display:none" name="Submit" value="下一页" />
<input name="Submit3" type="submit" value="打印" class="btn">
                    </div>
 
    </td>
  </tr>-------------
function show_select_list(ID,ID2,ID3,tagName,ID3_value){
//display
if(document.getElementById(ID).style.display=="none"){
document.getElementById(ID).style.display="block";
}else{
document.getElementById(ID).style.display="none";
}
document.getElementById(ID).onclick=function(){
document.getElementById(ID).style.display="none";
}
//width
var tagName=document.getElementById(ID).getElementsByTagName(tagName);
var tagL = tagName.length;
if (tagL>0) 
{
var tagW = tagName[0].innerHTML.length

for (var i = 1; i < tagL; i++){

if(tagW<=tagName[i].innerHTML.length){
var reg = /[^\u4e00-\u9fa5]/;
if(reg.test(tagName[i].innerHTML)){
tagW=parseInt(tagName[i].innerHTML.length)/2+2;
}else{
tagW=parseInt(tagName[i].innerHTML.length);
}
}

}

document.getElementById(ID).style.width=tagW*12+20+"px";
document.getElementById(ID3).style.width=tagW*12+"px";
} //text
for(var i=0;i<tagName.length;i++){
tagName[i].onclick=function(){
document.getElementById(ID3).innerHTML=this.innerHTML;
getAllValue(ID3,ID3_value);
}

}
}
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