Installing Rails 2 from Gem

I am a bit confused on how to install Rails 2 as a gem. When I run 'sudo gem install rails --source http://gems.rubyonrails.org' it pulls down version 1.2.5.7919'. Is this the same as Rails2? I don't think so ... anyway, it seems that the only way I could get Rails 2 down was to check out the trunk (or the 2-0-0_PR tag) from svn.

install like this gem install -v=RAILS_VERSION rails

Hmmm ... I am not sure what version to specify ... the following does not work ...

sudo gem install rails --version '> 1.2.5.7919' --source http://gems.rubyonrails.org ERROR: While executing gem ... (Gem::GemNotFoundException)

    Could not find rails (> 1.2.5.7919) in any repository

I cannot seem to find any version (I tried specifying 2.0.0, '>= 2', etc.) that works.

Well Rails 2.0 doesn't exist yet, it's getting close but it's not yet here.

AFAIK, the 1.2.5 gem is a packaged version of some recent snapshot of trunk.

And I'm reasonably sure that you can determine the difference between the 1.2.5 gem and the current state of edge rails with

$ svn diff http://svn.rubyonrails.org/rails/trunk http://svn.rubyonrails.org/rails/tags/rel_1-2-5