Back to the usual stuff here.
I started to learn ruby a while ago, and it was only for the sake to try out Ruby on Rails. The first step is to install and prepare everything for rails, which require some tweak because I am using the Ruby Version Management tool (rvm). For that, I just followed instructions there, and basically, one has just to set up the rails environment :
$ rvm use --create 1.9.2@rails3
and install rails and reguired gems :
$ gem install sqlite3-ruby
$ gem install rails
make this environment the default :
$ rvm 1.9.2@rails3 --default
and then start playing with RoR.