Got something working with mounting evergreen in a Rails 2.3 app.

README.rdoc

@@ -71,14 +71,23 @@ There's a rake task provided for you that you can use to run your specs:
 
     rake spec:javascripts
 
-== Integrating with Rails 2
+== Integrating with Rails 2.3
 
 Add the following line to your Rakefile:
 
     require 'evergreen/tasks'
 
-This will give you the `spec:javascripts` rake task. Note that mounting is not
-possible under Rails 2 and that `require 'evergreen/rails'` will fail.
+This will give you the `spec:javascripts` rake task.
+
+To mount the spec runner, add the following to your config/environments/development.rb file:
+
+    config.after_initialize do
+      require "evergreen/rails2"
+      config.middleware.insert_before "ActionController::Failsafe", "Evergreen::Rails2"
+    end
+
+Start your rails application and navigate to /evergreen. You should now see a
+list of all spec files, click on one to run it.
 
 == Configuration
 

lib/evergreen/rails2.rb

@@ -0,0 +1,41 @@
+require "evergreen"
+
+module Evergreen
+  class UrlPrepender
+    def initialize app
+      @app = app
+    end
+
+    def call headers
+      status, headers, body = @app.call headers
+      new_body = ""
+      body.each do |part|
+        new_body << part
+      end
+
+      new_body.gsub! /(src|href)="\//, '\1="/evergreen/'
+      [status, headers, [new_body]]
+    end
+  end
+
+  class Rails2
+    def initialize app
+      @app = app
+    end
+
+    def call headers
+      builder = ::Rack::Builder.new do
+        map "/evergreen" do
+          use UrlPrepender
+          run Evergreen::Application
+        end
+      end
+
+      if headers["PATH_INFO"].starts_with? "/evergreen"
+        builder.call headers
+      else
+        @app.call headers
+      end
+    end
+  end
+end