[CentOS] Postgresql uses sockets - but I'd like to use TCP/IP

Hi Folks,

CentOS 5.5 - Postgresql 8.4

Installed - startet

try to

 createuser -d- -a -p username 

get message

	could not connect to server: Connection refused
        	Is the server running locally and accepting
        	connections on Unix domain socket "/tmp/.s.PGSQL.0"?

postrgesql.conf has line 

 listen_addresses = '192.168.0.2'

Why sockets (in /tmp are  s.PGSQL.5431 )

What goes wrong?

I have an other installation on other server with same conf. Files.
There works all as I expect (no socket).

Any hints welcome

Thx
Timothy