installing rails2 with existing rails3

hello all,
i am working on rails3 currently... and now i need rails2 as well ..how
to install rails2 with existing rails3.
  i tried using rvm but getting the error as rvm command not found
even after installing it...

On which Os you are working

If on Ubuntu Edit your bashrc file

rvm is the way to do it. Make sure you have followed carefully the
instructions for installing it, dependent on your operating system.

Colin