Thaks for your responses. Rachel  Zakhem from the Computer Store 
followed up with Microsoft. This is the response that makes sense:

"Internal or external is more of a definition of user-type.  Internal 
requires CALs for employees to access, but that access may be from 
anywhere.  External does not require CALs because it is for access by 
non-employees, i.e. students or the general public.  You cannot purchase 
the external license for use by employees.  It is really a 
differentiation for the purposes of licensing the product."


-- 
Oscar Castaneda
Michigan State University