Update multiple model in one form

my project works like this the user will sign up first.after sign up
he/she will edit his profile.I use restful authentication plugins for
sign up.
model
class User < ActiveRecord::Base
has_one :profile
end

class Profile < ActiveRecord::Base
belongs_to :user
end

user controller
def create
cookies.delete :auth_token
@user = User.new(params[:user])
@user.save

@profile = Profile.new
@profile.user_id = @user.id
@profile.save
end
def edit
@user = User.find(params[:id])
end

migration
class AddProfileTable < ActiveRecord::Migration
def self.up
create_table :profiles do |t|
t.string :lastname
t.string :firstname
t.integer :user_id

end

end

def self.down
remove_table :profiles
end
end
edit form

Editing user

<%= error_messages_for :user %>

<% form_for(@user) do |f| %>

Name
<%= f.text_field :login %>

Email
<%= f.text_field :email %>

<%= f.submit "Update" %>

<% end %>

my problem, how to add the lastname and firstname on the form and update
the model profile?and what the method update?