U.Helper

Написано символов:<input name="fcounter" type="text" class="codeButtons" size="6" value="0" readonly="true">
  <script language="JavaScript" type="text/javascript">  
function chklen()  
{  
min_limit=0;  

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

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

document.addform.fcounter.value = (min_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>

Символов введено: <span id="apoid">0</span>
<script>
$(document).ready(function() {
  $('textarea[name="message"]').keyup(function() {
   $('#apoid').html($(this).val().length);
  });
});
</script>