Install RoR 2.1

Download the source package from http://www.ruby-lang.org/en/downloads/, unpack the tar.gz file, and follow the README file.

Rubygem

Download from RubyGems, extract it, and run "sudo ruby setup.rb".

Then you can start the gem server by calling "gem server". And you can view the server via http://localhost:8808.

Install Rails through Rubygem

Run "sudo gem install rails".

Upgrade from RoR 2.0

If you are upgrading from RoR 2.0, there are a few gotcha.

Rolling with Rails 2.1 is a good start. A Rails 2.1 case study: upgrading the Insoshi social networking platform might be your next reference.