Can anyone tell me which RailsInstaller version was the last one that provided Rails 2.3.x ?
The release notes are a bit skimpy 
but I need to help someone
on Windows get set up to work on a legacy app.
TIA,
You can use latest RailsInstaller and install Rails 2.3.x:
gem install rails -v 2.3.14
Then use a RubyGems trick to use one specific version of rails command line utility:
rails _2.3.14_ myapp -d sqlite3
In that scenario, I recommend you add Bundler to it:
http://gembundler.com/rails23.html
That way will be more easy for you to handle both versions of Rails.
Hope that helps,