How to install ruby 1.9 and rails with RVM

Just follow these steps

ruby -v
mkdir -p ~/.rvm/src/ && cd ~/.rvm/src && rm -rf ./rvm/ && git clone git://github.com/wayneeseguin/rvm.git && cd rvm && ./install
rvm install 1.9.1
rvm list
rvm 1.9.1
rvm 1.9.1 --default
rvm system
gem install tzinfo builder memcache-client rack rack-test rack-mount erubis mail text-format thor bundler i18n
gem install rails --pre
rails topscore
cd topscore
rails server
gem install sqlite3-ruby
rails generate scaffold game name:string
rake db:migrate

and you are done :)
taken from http://railscasts.com/episodes/200-rails-3-beta-and-rvm