http://ckeditor.com/

See the forum post at
http://platon.sk/forum/projects/viewtopic.php?t=1131749
which reads approximately as

david803 / Posted: 10 May 2010 08:20

My CKEditor version is 3.0.1

Step 1. line 1047 and line 1195 :
echo '<textarea class="',$css_class_name,'" name="',$this->cgi['prefix']['data'].$this->fds[$k],'"';

Change to:
echo '<textarea ';

if (isset($this->fdd[$k]['textarea']['id'])) {
	echo 'id="',$this->fdd[$k]['textarea']['id'],'" ';
}

if (isset($this->fdd[$k]['textarea']['class'])) {
	echo 'class="',$this->fdd[$k]['textarea']['class'],'" ';
}else{
	echo 'class="',$css_class_name,'" ';
}

echo 'name="',$this->cgi['prefix']['data'].$this->fds[$k],'"';

Step 2. Add "ckeditor.js" path, like this:
<script type="text/javascript" src="editor/ckeditor/ckeditor.js"></script>

Step 3. use like this:

$opts['fdd']['myField'] = array(
	'maxlen'   => 65535,
	'name'     => 'Memo',
	'select'   => 'T',
	'sort'     => false,
	'textarea' => array('id' => 'myField', 'class'=> 'ckeditor', 'rows' => 5, 'cols' => 50)
);