I have a Ubuntu rails enviroment for playing around with ROR. Right now I am running Rails 2.3.8.
I want to look into rails 3. Is it possible to run both dev enviro
I would highly recommend Ruby Version Manager (rvm) - see this railscast for more information. This allows you to easily manage different versions of Ruby on the same machine. I believe this should also enable you to keep the different versions of Rails separate from each other, and allow you to switch between them easily - see this example from http://rvm.beginrescueend.com/gemsets/basics/ :
rvm 1.9.2-head
gem install rails -v 2.3.3
rvm gemset create rails222 rails126
Gemset 'rails222' created.
Gemset 'rails126' created.
rvm 1.9.2-head@rails222
gem install rails -v 2.2.2
rvm 1.9.2-head@rails126
gem install rails -v 1.2.6
Hope that helps!