I just tried to get postgres working under Ubuntu 12.10 and had to google a few things, so here is a quick note of how to get it running:
Install postgres:
apt-get install postgresql-9.1
Change password for the postgres user:
sudo passwd postgres
Open the file /etc/postgresql/9.1/main/pg_hba.conf and change the line:
local all all peer
to
local all all md5
Create a database user (-P for password prompt):
sudo -u postgres createuser -P someusername
Create a database (-O specifies the owner):
sudo -u postgres createdb -O somedatabasename
Restart postgres:
sudo service postgresql restart
Start setting up the new database with the new user:
psql -U someusername -d somedatabasename
When in the psql terminal use \? to list all available commands and \q to exit.