Create a script that includes the resources of a project

require 'path/to/rails_root/config/boot'
require 'path/to/rails_root/config/environment'
require 'irb/completion'
require 'console_app'
require 'console_sandbox'
require 'console_with_helpers'
...

you probably want to specify this on the command-line to irb like
script/console does.

Take a look at /path/to/lib/ruby/gems/1.8/gems/rails-1.x.x/lib/
commands/console.rb for more info