<div onKeyUp="chklen()">     
   $_MESSAGE$     
   </div>     
   <b>Осталось символов:</b> <input name="fcounter" type="text" class="codeButtons" size="6" value="40000" readonly="true">

<script language="JavaScript" type="text/javascript">     
   function chklen()     
   {     
   max_limit=40000;     

   str = document.addform.message.value;     
   len = str.length;     

   if (len > max_limit)     
   {     
   str = str.substring(0,max_limit);     
   len = str.length;     
   document.addform.message.value = str;     
   }     

   document.addform.fcounter.value = (max_limit - document.addform.message.value.length);     

   while ( document.addform.fcounter.value<0)     
   {     
   document.addform.message.value = str.substring(0,len-1);     
   str = document.addform.message.value;     
   len = str.length;     
   document.addform.fcounter.value = (max_limit - document.addform.message.value.length);     
   }     
   }     
   </script>