如何判断<div>的打开关闭状态？

<SCRIPT language=Javascript>
<!--
var old_Lay=1;
function onChangeXc(j){
try{
   var obj=document.getElementById("man" + j);
   if(j!=old_Lay){
       var obj1=document.getElementById("man" + old_Lay);
       obj1.style.display="none";
   old_Lay = j;
       }
   if(obj.style.display=="none"){  obj.style.display="";   }
  else{ obj.style.display="none"; }
  }
catch(e) {}
}//-->
</SCRIPT>
<table width="100%" border="0" cellspacing="0" cellpadding="0" align="center">
   <tr>
      <td width="20%">&nbsp;</td>
      <td width="80%" align="left" valign="top"><table width="100%" border="0" cellspacing="0" cellpadding="0" align="left">
        <tr> 
         <td height="21" valign="top"><img border="0" src="image/upload.gif" width="16" height="16"><A href="javascript:onChangeXc(1)"><font size=3>信息中心</font></A>
           <BR><DIV id="man1" style="DISPLAY: none"> 
           &nbsp;&nbsp; <a href="#">审核账户</a><BR>
           &nbsp;&nbsp; <a href="#">申请账户</a><BR>
          </div></td>
        </tr>
        <tr> 
         <td height="21" valign="top"><img border="0" src="image/upload.gif" width="16" height="16"><A href="javascript:onChangeXc(2)"><font size=3>帐号管理</font></A>
           <BR><DIV id="man2" style="DISPLAY: none"> 
           &nbsp;&nbsp; <a href="bbs_use_se.asp">查看账户</a><BR>
           &nbsp;&nbsp; <a href="bbsbzgl.asp">BBS版主管理</a><BR>
           </div></td>
        </tr>
</table>