I am using debian, so here are a few commands I use:
# apt-get install postgresql
# sudo su - postgres
# createuser /your_login/
# apt-get install ruby
# apt-get install libpgsql-ruby
# apt-get install irb
# apt-get install libredcloth-ruby
# apt-get install rdoc

-> why???
# ln -s /sbin/ifconfig /bin/

# gem install -r rails
Only if you expect to develop and release:
# gem install -r meta_project


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

Change config/environment.rb to set the domain, default is something like
'leparlement.org', define it as your web site or email domain.

In procmail, define a rule to redirect the relevant mail to parlement, I use:
:0 c
* ^TO parlement|leparlement.org
| /home/manu/parlement/trunk/script/runner 'Mailman.receive STDIN.read'


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


Now you can go to localhost:3000