map.namespace(:admin)...

Its fairly simple, the API docs for it aren't too bad
http://api.rubyonrails.org/classes/ActionController/Routing/RouteSet/Mapper.html#M000351

Easiest thing would be to write something like

map.namespace(:admin) do |route|
  route.resources :articles
end

then run the `rake routes` task to see what it effectively generates

Geoff