I have tried installing Ruby 2.0.0 using RVM:
Ruby 2.0.0
RVM
rvm install 2.0.0
Once installation is done. I did rvm list
rvm list
You can do rvm use 2.0.0.
rvm use 2.0.0
If it tells you that you have it not installed, you just do:
rvm install ruby-2.0.0-p598
It will install everything that you need for you and then you can select which version of Ruby to use with rvm use
rvm use