User attributes

I am using PostgreSQL ver 6.5 on Redhat 6.1 and have 2 users that cannot
perform the same functions as other users in the database. I am looking for
a tool that will let me compare the records/attributes of 2 existing users
(so I can see what the differences are and change the 2 new users to match
the existing ones).

I have read about ALTER USER, but that assumes you already know what you
want to alter.
Any suggestions on how to compare 2 users will be greatly appreciated.

TIA-
Jim