Rails comes preinstalled on Leopard, but the preinstalled version is
1.2.3. However, RubyGems is also preinstalled, and you can use gem to
upgrade to rails 2.
gem update --system (updates RubyGems itself)
gem update (updates all your gems, including rails)
rails 2 depends on a new gem, activeresource, that rails 1.2 didn't, so:
gem install activeresource
You can find your gems in /usr/lib/ruby/user-gems/ (which is actually
a symlink to /Library/Ruby/Gems)
As far as rails is concerned updating the preinstalled gems is more or
less what I did on my mac mini, which I did a clean Leopard install
on. On my macbook, I upgraded from Tiger, where I had the rails stack
set up according to the guide at hivelogic.
After the upgrade to Leopard, mysql wasn't working, so I built it from
source, following this guide:
I haven't checked if mysql released a leopard installer since.
Hope that helps