Hello -
think I found the solution (works for me, anyway):
locate the file: catalog/admin/information_form.php
in this file, find
<td class="main" valign="top"><?php echo tep_draw_textarea_field('information_description[' . $languages[$i]['id'] . ']', '', '100', '20',
(somewhere about line 94)
after '100', '20', add: 'mceEditor',
(beware not to accidentially delete any of the following code)
Save back to server - It should work now. If you want, you can also change the size of the editor field by changing the 100 (width) and the 20 (height).
Good luck!
Boghandler