<input type="checkbox" id="chkWhatever" onclick="chkWhatever_onclick()">


<SCRIPT language="javascript">

   function chkWhatever_onclick()
   {
       try
       {
           /// Something like this
           txtMyTextBoxToDisable.disabled = !chkWhatever.checked;

       }
       catch(e)
       {
            throw(e);
       }

   }

</SCRIPT>