[INIMSS] problem with user privileges

Hi,

I am trying with the user privileges in postgresql-7.1.3-1PGDG on RedHat 7.1 .

I followeb this procedure;
foo$ psql template1 postgres
template1=# create user dba with createdb createuser;
template1=# \q
foo$ psql template1 dba
template1=# create database mydb;
template1=# \q
foo$ psql mydb dba
mydb=# create table table_a (id int primary key, name char(10));
mydb=# create user dbu1;
mydb=# grant select,insert on table_a to dbu1;

Up to this all are working as expected. The user dbu1 can make only SELECT
and INSERT on table_a.

Then I added one more user (dbu2) using the command at psql prompt.
mydb=# create user dbu2;

When connected to the DataBase mydb as dbu2, the user cannot create database
on perform operations on table_a, but can create new tables and he has full
control over it.

Is there any way to prevent such a situation by revoking the permissions of
the user dbu2 on the database, so that he will not be able to connect to the
database?

Thank You

Dino