Removing Users and Revoking Privileges

To All,

I am running Postgres version 7.4.19.

One thing I wanted to do and have successfully completed is changing the
ownership of a Postgres database and all of its tables to a new owner.
I have also successfully granted access privileges to the new owner.

What I have been unable to do successfully is to remove two users who
should no longer have access to the database or its tables. As super
user postgres, I have attempted to REVOKE access privileges for those
two users, but to no avail. The REVOKE command appears to work and does
not generate an error message, however, upon inspection the two users
remain and continue to have all of the same access privileges they had
before executing the REVOKE command.

I do not know what user originally created the database. I have though
attempted to revoke privileges as not only user postgres, but also as
the new owner of the data base, as well as both of the two users for
which I wish to revoke access privileges.

The two users I want to remove or, at least revoke privileges for, are
also associated with other databases, so I don't believe I can simply do
a DROP USER. If I do that, I may wind up negatively impacting other
Postgres databases.

Let me know, if you have any ideas.

Thanks