Question on Rails application design

I am following the Agile Development with Ruby on Rails, both the Beta
and the First Edition Books, and I was wondering something. I am working
on a simple book-management aplication for our software development
firm. It will be used strictly by some 20-30 offline computers, with
only an administrator that will be adding, auditing and deleting books
from the database, and an employee who can access a list of books and
can choose some to borrow and/or download them if they are available in
pdf format. My question is, should I create three models, one that is
for the startup screen, a menu with an Administrator Login or General
Employer Acces, another model for the Administrator called “Admin”
Model, and the last one named “User” Model for the employer who only can
update the list of books or mark/unmark them borrowed. Problem is, do I
need three models? Menu, Admin and User? Now I know that a model is in
direct connection with the database so I thought that the “Menu” model
might not be worth the time, but how can I offer the chance for the poor
admin to login? Should I add a controller to the “Admin” model that
sends him to an index with a login menu?