Help me start postmaster on a default installation of PostgreSQL.

Hi!
I'm running Ubuntu 10.10 and I have installed PostgreSQL and JDBC
drivers form the repository. I have not changed any default settings. I
want to run the postmaster service to access database from a Java
program. I've read around a bit about and it has not helped. I don't
want to go in great depth about how to do this because right now I'm
focusing on learning Java and I don't really have enough time to read
hundreds of pages of docs.

I've added /usr/lib/postgresql/8.4/bin to my PATH variable.

Command "pg_ctl start" or "postmaster" gives an error about not being
able to find "postgresql.conf" in the directory specified by PGDATA or
my home folder if it's blank.

I found this file (postgresql.con) in /etc/postgresql/8.4/main/ and
created a shortcut to it in my home folder.

Now I'm getting error

2011-07-06 09:56:57 GMT FATAL: data directory
"/var/lib/postgresql/8.4/main" has wrong ownership
2011-07-06 09:56:57 GMT HINT: The server must be started by the user
that owns the data directory.

This data directory is owned by postgres.

I read somewhere that this postmaster has to be run by the user postgres
but I don't know how to do that.

Apart from that my installation is working fine. I've already created a
user for myself and a small trial database too.

Please help me.