index.html.erb

<%= embed_action :controller => 'roman_embedded', 
                 :action => 'index' %>

roman_embedded_controller.rb

class RomanEmbeddedController < ApplicationController
  
  def index
    render :text => 'HELLO WORLD'
  end
  
end

roman_tests_controller.rb

class RomanTestsController < ApplicationController
  
  def index
    render :action => 'index', :layout => false
  end
  
  def another
    embed_action :controller => 'roman_embedded', 
                 :action => 'index'
  end
  
end

routes.rb

ActionController::Routing::Routes.draw do |map|
  map.connect "/roman_tests/index", :controller => 'roman_tests', :action => 'index'
  map.connect "/roman_tests/other", :controller => 'roman_tests', :action => 'another'
end