The following articles were useful:
  1. get Postgres working on Linux  copy on VII.2012
  2. PostgreSQL installation  copy on VII.2012
Basically, you just have to follow the instructions on the first article and you're done. The second article is just for additional reference (I didn't have to use any of the commands found there). The only difference are that I used the "-d" switch at the "createuser" command (instead of the "-D" switch), as I wanted my new user to be able to create databases. Also the instructions mention that the user you create with:
            sudo -u postgre createuser -D -P someuser
can't connect to the database, which is misleading if the user happens to be a local Linux user (apparently these users can authenticate with the "peer" mechanism). But if you chose any other name then you indeed have to edit /etc/postgresql/9.1/main/pg_hba.conf file to change the "local all all peer" line to "local all all md5".

To create the database, after I created a user "hr", I did a:

psql -U hr createdb myhr
Note: if you haven't or don't want to set the line "local all all peer" to "local all all md5", a less intrusive solution is to add the following line:
local all hr md5
I.e. change the authentication method just for the "hr" user. Afterwards, one can create a new database (say "masterdet") by connecting as user "hr" without having to use the option suggested in the article (masquareding as user "postgres" by running the "createdb" command under a "sudo -u postgres". What I basically did to create a new database was:
createdb -U hr -O hr masterdet
Finally, instead of the:
sudo apt-get install postgresql-9.1
line, a simpler:
sudo apt-get install postgresql
will do (gets the latest).