Postmaster.pid & Unix domain socket errors, OS X

I've checked the archives at
And Apple's documentation at
http://developer.apple.com/internet/macosx/postgres.html
And the article at www.macdevcenter.com, as well as the available info at
Techdocs.postgresql.org

I have successfully installed PostgreSQL 7.3 for Mac OS X (10.2.4) and can
successfully start postgresql - it returns the message "postmaster
successfully started."
However, when I try to create a database ("createdb mydb")
I get the error:
psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

I am only trying to use a localhost connection (no TCP/IP), for
learning/development purposes. I shut off my software firewall (though I
shouldn't have to, right ?), and that made no difference.
I checked & rechecked the pg_hba.conf and postgresql.conf files. Another
troubling thing, is that when I try to restart (thinking I probably should,
after config changes !), with the command: pg_ctl reload
I get the error message, "pg_ctl: cannot find
/usr/local/pgsql/data/postmaster.pid Is postmaster running?"

So, I don't know where to go from here. I have verified permissions on
the /usr/local/pgsql directory (did a chown -R ), and made sure to add the
paths
setenv PGDATA /usr/local/pgsql/data
setenv PATH ${PATH}:/usr/local/pgsql/bin
To my .tcshrc file, and some of the aliases I've setup in there (for other
unrelated commands) do work fine.

I am of course admitting that I'm _completely_ new to this. Please help
(!)