1. Download "tiny_mce" from http://tinymce.moxiecode.com/
2. Copy the download /jscripts/tiny_mce to [OSC_ROOT]/iadmin/includes/javascript/tiny_mce
3. Edit: /iadmin/includes/header.php

ADD AT TOP:

<script language="javascript" type="text/javascript" src="/portal/includes/javascript/tiny_mce/tiny_mce.js"></script>
<script language="javascript" type="text/javascript">
tinyMCE.init({
mode : "textareas"
});
</script>

---

To add buttons in the panel, simply use:

tinyMCE.init({
...
theme_advanced_buttons1 : "separator,insertdate,inserttime,preview,zoom,separator,forecolor,backcolor",
theme_advanced_buttons2 : "bullist,numlist,separator,outdent,indent,separator,undo,redo,separator",
theme_advanced_buttons3 : "hr,removeformat,visualaid,separator,sub,sup,separator,charmap"
});

Details: http://wiki.moxiecode.com/index.php/TinyMCE:Configuration/theme_advanced_buttons_1_n