Well, now that the new version of ruby on rails is out(2.0.2), everything should be new and improved. I do like a lot of things in the new version of rails but many of my apps are written in previous versions(like 1.2.6) and I'd like to keep them that way, for now. Rails 2.x is pretty good, but it's missing a lot of old rails core commands(like the old rest-less script/generate scaffold), that I happen to use sometimes. Also, a lot of people deploy rails applications in shared hosting environments and other places where they don't have the permissions to reinstall old versions of rails via gem, so here's an alternative. Here we will actually freeze the older version of rails to our application. In this example, I'll be downgrading ruby on rails 2.0.2 to 1.2.6. 

First, create a new rails application(we'll call it app):

     $ rails app

Then, cd into the directory:

     $ cd app

Now we will download the version of rails you want(here we will grab 1.2.6, but you can get any version) from the rails archive:

Note: you can do this a couple of different ways, this is using svn

     $ svn co http://dev.rubyonrails.org/svn/rails/tags/rel_1-2-6/

Copy and rename the downloaded folder to vendor/rails: 

     $ mv rel_1-2-6/ vendor/rails

Note: Rails looks automatically for a vendor/rails folder before using the server-wide ruby on rails libraries(aka gems). Having them stored this way is called "freezing" your gems.

Now all we have to do is replace the 2.0.2 version of  config/environment.rb file with a copy of the 1.2.6 version:  

     $ mv config/environment.rb config/environment.rb.original

     $ nano -w config/environment.rb

Here I'm using the linux text editor, nano. You can also use emacs, vi, notepad, textpad, or whatever you want. Basically, we're going to create a new empty file named config/environment.rb and paste this code into it:

That's it! You can now confirm that your using rails 1.2.6 by running this command:

      $ script/about

 You should see the version of rails now being 1.2.6, like so: