Use RTE in the comments form

{exp:comment:form channel="blog" preview="channel/preview"}
  <label for="comment">Comment:</label>

  <textarea name="comment" cols="70" rows="10">{comment}</textarea>
  <label><input type="checkbox" name="notify_me" value="yes" {notify_me} /> Notify me of follow-up comments?</label>

  <input type="submit" name="submit" value="Submit" />
{/exp:comment:form}