[kostr]

У вас jquery подключена?

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js"></script>
<script type="text/javascript">

function setCookie(name, value, expiredays, path, domain, secure) {
 if (expiredays) {
  var exdate=new Date();
  exdate.setDate(exdate.getDate()+expiredays);
  var expires = exdate.toGMTString();
 }
 document.cookie = name + "=" + escape(value) +
 ((expiredays) ? "; expires=" + expires : "") +
 ((path) ? "; path=" + path : "") +
 ((domain) ? "; domain=" + domain : "") +
 ((secure) ? "; secure" : "");
}
function getCookie(name) {
 var cookie = " " + document.cookie;
 var search = " " + name + "=";
 var setStr = null;
 var offset = 0;
 var end = 0;
 if (cookie.length > 0) {
  offset = cookie.indexOf(search);
  if (offset != -1) {
   offset += search.length;
   end = cookie.indexOf(";", offset)
   if (end == -1) {
    end = cookie.length;
   }
   setStr = unescape(cookie.substring(offset, end));
  }
 }
 return setStr;
}
function block_now(id) {
 if(getCookie(id) == 1) {
  $('#' + id).stop().slideUp();
  setCookie(id, 0, 90, "/");
 } else {
  $('#' + id).stop().slideDown();
  setCookie(id, 1, 90, "/");
 }
}
function block_start(id) {
 var cookie_stat = getCookie(id);
 if((cookie_stat == 1) || (!cookie_stat)){
  display = '';
 } else {
  display = 'none';
 }
 document.getElementById(id).style.display = display;
}
</script>

<table>
<tr onClick="block_now('blok_1')" style="cursor:pointer;">
 <th>Заголовок блока</th>
</tr>
<tr>
 <td>
<div id="blok_1">
  Содержимое блока <br>
  Содержимое блока <br>
  Содержимое блока <br>
  Содержимое блока <br>
  Содержимое блока
</div>
 </td>
</tr>
</table>

<script>
 block_start("blok_1");
</script>