multiple applications sharing models

[eluser]jmb727[/eluser]
I want to develop my own CMS using CodeIgniter and I've got two application folders, for the frontend and backend respectively.

Code:

admin/
   backend/
   .htaccess
   index.php
frontend/
system/
user_guide/
index.php

Backend/ and Frontend/ are application directories.

Is this the best way to achieve this? also, i imagine the backend and the frontend applications sharing certain components & resources (css files, models, maybe other stuff to), how could i achieve this?

Thanks.