Postgresql Novice problem

Hello,
        I installed Postgresql on my machine under Mandrake 10.0. I'm using
unixODBC
front end to create a database. I defined a User DSN and here is what I got
from the .odbc.init file:

[MyNewDatabase]
Description             = PostgreSQL
Driver          = PostgreSQL
Trace           = No
TraceFile               =
Database                = newDb
Servername              = localhost
Username                = newuser
Password                = newpassword
Port            = 5432
Protocol                = 6.4
ReadOnly                = No
RowVersioning           = No
ShowSystemTables                = No
ShowOidColumn           = No
FakeOidIndex            = No
ConnSettings            =

But when a I try to use the Datamanager to get access to the database, it's
looks impossible. I got an error message: [unixODBC]FATAL: IDENT
authentication failed for user "newuser".

Do anyone have an idea how to solve my problem?

Best regards,
Alain-Serge