Help using a single form to update three models

Really hoping someone on this forum can help me out - any help is
greatly appreciated.

I have been through the Ryan B railcasts and tutorials on using a
single form to update more than one model. They are all based on the
concept of having Project model that has many Tasks. The application
I am working on requires a third level of model added to the form so
Projec has many Tasks and Task has many Task Details. I can display
the form in the "new" action so that all fields show up and it appears
right. However, I can not get the "create" to work, not sure if the
problem is "create" in my controller, or the hash being created in my
fields_for tag.

class Project < ActiveRecord::Base
has_many :tasks

def task_attributes=(task_attributes)
  task_attributes.each do |attributes|
    tasks.build(attributes)
  end
end
end

class Task < ActiveRecord::Base
has_many :task_details
belongs_to :projects

def task_detail_attributes=(task_detail_attributes)
  task_detail_attributes.each do |attributes|
    task_details.build(attributes)
  end
end

end

class TaskDetail < ActiveRecord::Base
belongs_to :tasks
end

class ProjectController < ApplicationController

def index
  @projects = Project.find(:all)
end

def new
  @project = Project.new
  @project.tasks.build
  @task = Task.new
  @task.task_details.build
end

def create
  @project = Project.new(params[:project])
  @task = Task.new(params[:task])
  params[:task].each_value { |task_detail|
@task.task_details.build{task_detail} }
  if @project.save and @task.save
    flash[:notice] = "Successfully created project."
    render :action => 'index'
  else
    render :action => 'new'
  end
end

end

<% form_for :project, :url => { :action => :create } do |f| %>
  <p>
    Name: <%= f.text_field :name %>
    Date: <%= f.date_select(:date) %>
  </p>
  <% for task in @project.tasks %>
    <% fields_for "project[task_attributes][]", task do |task_form| %>
      <p>
        Name: <%= task_form.text_field :name %>
        Description: <%= task_form.text_area :description %>
        Fixed Task: <%= task_form.check_box :fixed_flg %>
      </p>
   <% end %>

   <% for task_detail in @project.tasks %>
     <% fields_for "task[task_detail_attributes][]", task_detail do |
detail_form| %>
       <p>
       Sub Task: <%= detail_form.text_field :sub_task %>
       Assigned: <%= detail_form.check_box :assigned_flg %>
       </p>
      <% end %>
    <% end %>
   <% end %>

<p> <%= submit_tag "Create Project" %> </p>
<% end %>