Simple relation question

Hello group,

I'm new to Rails and i'm trying to create a 'nested' form for user to
a company. I would like the client to be able to create a company in
the users sign up form. I get the part were you can choose a company
from a collection, but i want to allow the user to create a new
company through a text field in the sign up user form.

This is what i have:

class User < ActiveRecord::Base
  belongs_to :company
  has_one :company

attr_accessible :email, :password, :password_confirmation, :remember_me, :admin, :company_id, :firstname, :lastname

  accepts_nested_attributes_for :company

class Company < ActiveRecord::Base
  has_many :users
  accepts_nested_attributes_for :users

  attr_accessible :name

    #validates_presence_of :name
    #validates_uniqueness_of :name

and in the form:

<%= simple_form_for(resource, :as => resource_name, :url =>
registration_path(resource_name)) do |f| %>
  <%= f.error_notification %>

  <div class="inputs">
    <%= f.fields_for :company do |cf| %>
      <%= cf.input :name, :required => true, :autofocus => true %>
    <% end %>
    <%= f.input :email, :required => true, :autofocus => true %>
    <%= f.input :password, :required => true %>
    <%= f.input :password_confirmation, :required => true %>

  <div class="form-actions">
    <%= f.button :submit, :class => 'btn-primary', :value => 'Sign up'
<% end %>

The above code gives a company name text field in the form but on
submit rails trows an error: Can't mass-assign protected attributes:
company. I probably have to add a route to? until now i only have
resources :companies and resources :users.

I did my best to google for a solution/ example.. found some nested
form examples but its not clear to me.

Any help on this would be appreciated.

Thanks in advance!