## user_controller.rb

 def signup
  case request.method
    when :post
     tpass=(rand(10000)+1000).to_s
     @user = User.new(params[:user])
     @user.update_attribute("password",tpass)  # Put the generated password
     if @user.save
       redirect_to :controller => 'user', :action => 'regconfirmation'
     end
  end
 end

 def regconfirmation
   ## show "tpass" to the user like: "Your generated password is: tpass"
 end

## regconfirmation.rhtml

<h1>Your registration has been completed successfully!</h1>

<p>Your login: <%= @tlogin %></p>
<p>Your pass: <%= @tpass %></p>