用javaScript控制DIV的显示
function showDiv(targetid)
{
   if (document.getElementById){
 
            var target=document.getElementById(targetid);
               alert(target.style.display);
            if (target.style.display =="block" || target.style.display == "" ){
            alert('block');
                target.style.display="none";
            }
            else if(target.style.display == "none")
            {
            alert('none');
            target.style.display = "block";
            }
   }
}

<form id="frm1" action="">

<td>
       <input type="text" name="caption" size="62" />
       <input type="button" name="annex" value="添加附件"
        onclick="showDiv('annexDiv');" />
       <form action="" id="frm2">
       <div id="annexDiv" style="display: none;">
     
        <input type="text" name="annex" size="62" />
        <input type="button" name="addAnnex" value="浏览" />
        <input type="button" name="delAnnex" value="删除" onclick="showDiv('annexDiv');" />
         </div>
         </form>
      </td>

</form>