postgres not accessible in Mandrake 9.0

I have trouble connecting to the postgres server in Mandrake 9.0.

The server is started by default on boot and when I try to access a database
created as "postgres user" within anouther user (e.g. "koegli") account, I get
the error:

FATAL ERROR: user koegli does not exist.

After I have created a user koegli from within psql logged in as postgres, I get
the error message that typically tells me that there couldn't be a server
connection established (classical for "-i" option missing). I then looked into
the postgres startup script and added the "-i" option to the startup command.
But now the server startup fails completely and no process "postmaster" is
running.

Has anyone encountered a similar problem with Mandrake before? I haven't had the
problem with my old SuSe distro.

Thanks for any help.

NICOLAUS