frame居中显示？


<div id="shoulderBar">
  <dl>
    <dd id="expo">2010年上海世博会开幕第 <span>
<script language="javascript">
var expo_start_date = new Date(2010, 04, 01); // 2010-5-1
var today = new Date();
var t = today.getTime() - expo_start_date.getTime();
var d =  Math.floor(t / (1000 * 60 * 60 * 24)) + 1;
document.write(d);
</script>
</span> 天</dd>
<%
Date d = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
        String date = sdf.format(d);
Calendar now = Calendar.getInstance();
//星期数，从星期天开始到星期六为0-7 
now.setTime(d);
now.get(Calendar.DAY_OF_WEEK);
int week=now.get(Calendar.DAY_OF_WEEK);
String   strWeek= " "; 
            switch(week){ 
                            case   1:   strWeek= "星期日 "; 
                                            break; 
                            case   2:   strWeek= "星期一 "; 
                                            break; 
                            case   3:   strWeek= "星期二 "; 
                                            break; 
                            case   4:   strWeek= "星期三 "; 
                                            break; 
                            case   5:   strWeek= "星期四 "; 
                                            break; 
                            case   6:   strWeek= "星期五 "; 
                                            break; 
                            case   7:   strWeek= "星期六 "; 
                                            break; 
                            default:   strWeek= " "; 
            } 
%>
<dd><%=date%></dd>
<dd><%=strWeek%></dd>    <dd id="weather"><span>
<iframe src="http://m.weather.com.cn/m/pn2/weather.htm?id=101020100T " width="180" height="40" marginwidth="0" marginheight="0" hspace="0" vspace="8" frameborder="0" allowtransparency="true" scrolling="no"></iframe></span></dd>
  </dl>
  <div id="search">
    <ul>
      <li><span>全文检索</span></li>
      <li>
        <input name="textfield" type="text" class="search" id="textfield" value="请输入关键字" />
      </li>
      <li>
        <input name="button" type="submit" class="btn" id="button" value="" />
      </li>
    </ul>
  </div>
</div>
这个框架的文字怎么居中显示啊  dd标签里面设置么  还是iframe里面？