I am using debian, so here are a few commands I use:
# apt-get install ruby
# apt-get install postgresql
# apt-get install libpgsql-ruby1.6
# apt-get install libredcloth-ruby
# apt-get install irb


Once you have everything set up (ruby, postgresql, redcloth, irb), you can
launch parlement thus:
~ cd parlement
~ psql -q template1 -f db/schema.sql
~ ruby lib/data_import.rb
~ ruby ./script/server

The database is setup for user "manu", you may need to change the file
config/database.yml for your own settings.

Now you can go to localhost:3000