Error while installing Ruby 1.9.3 and Rails 3.1.3 on Mac OS X Lion

I've an error when I want to install Ruby 1.9.3 on OS X. I've seen most of the problem come from xCode not being installed. So, I installed it and I still have the problem, so, here it is:

MacBook-Pro-de-Arnaud:~ Arnaud$ rvm install 1.9.3 Installing Ruby from source to: /Users/Arnaud/.rvm/rubies/ruby-1.9.3-p0, this may take a >while depending on your cpu(s)... ruby-1.9.3-p0 - #fetching ruby-1.9.3-p0 - #extracted to /Users/Arnaud/.rvm/src/ruby-1.9.3-p0 (already extracted) Fetching yaml-0.1.4.tar.gz to /Users/Arnaud/.rvm/archives Extracting yaml-0.1.4.tar.gz to /Users/Arnaud/.rvm/src Configuring yaml in /Users/Arnaud/.rvm/src/yaml-0.1.4. Compiling yaml in /Users/Arnaud/.rvm/src/yaml-0.1.4. Installing yaml to /Users/Arnaud/.rvm/usr ruby-1.9.3-p0 - #configuring ERROR: Error running ' ./configure --prefix=/Users/Arnaud/.rvm/rubies/ruby-1.9.3-p0 --enable-shared --disable-install-doc --with-libyaml-dir=/Users/Arnaud/.rvm/usr ', please read /Users/Arnaud/.rvm/log/ruby-1.9.3-p0/configure.log ERROR: There has been an error while running configure. Halting the installation. 

So, I decide to let the 1.8.7 and direct go to Rails and the install seems to go well, but nothing is istall :/

MacBook-Pro-de-Arnaud:~ Arnaud$ sudo gem install rails Password: Successfully installed rails-3.1.3 1 gem installed Installing ri documentation for rails-3.1.3... Installing RDoc documentation for rails-3.1.3... MacBook-Pro-de-Arnaud:~ Arnaud$ gem list *** LOCAL GEMS *** MacBook-Pro-de-Arnaud:~ Arnaud$ rail -bash: rail: command not found MacBook-Pro-de-Arnaud:~ Arnaud$ rails /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:777:in `report_activate_error': Could not find RubyGem rails (>= 0) (Gem::LoadError) from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:211:in `activate' from /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/rubygems.rb:1056:in `gem' from /usr/bin/rails:18 

Would anyone have a solution ?