rescue_404.rb

# Put this in routes.rb at the very bottom (right before end)

map.error '*path', :controller => 'application', :action => 'rescue_404'

# Put this in application.rb

rescue_from ActiveRecord::RecordNotFound, ActionController::UnknownAction, :with => :rescue_404

def rescue_404
  render :template => "errors/404", :layout => "application", :status => "404"
end