Installing Rails 3.0.x

$ mkdir rails30
$ cd rails30
$ bundle init
$ editor Gemfile
$ cat Gemfile
source 'http://rubygems.org'
gem "rails","3.0.10"
gem 'mysql2', '~> 0.2.11'
$ bundle install --path vendor
Fetching source index for http://rubygems.org/
Installing rake (0.9.2)
Installing abstract (1.0.0)
Installing activesupport (3.0.10)
Installing builder (2.1.2)
Installing i18n (0.5.0)
Installing activemodel (3.0.10)
...
$ bundle exec rails -v
Rails 3.0.10
# the following is to overwrite Gemfile that was originally created
$ bundle exec rails new ../rails30 -d mysql < /bin/echo "Y"
...
$ cat Gemfile
source 'http://rubygems.org'

gem 'rails', '3.0.10'

# Bundle edge Rails instead:
# gem 'rails', :git => 'git://github.com/rails/rails.git'

gem 'mysql2', '~> 0.2.11'

# Use unicorn as the web server
...