Rails form_tag form writing - with non-active record model

I'm somewhat of a Rails newbie. I'm writing a couchrest-rails app, so am not using activerecord for this model. I just figured out that that means that

form_for(@model) 

won't work. I'm trying to work out how to use form_tag -- but most of the examples don't involve new & create actions.

This is wrong:

<h1>New article</h1>

<% form_tag new_article_url(@article), :method => :post do |f| %>
  <%= f.error_messages %>

  <p>
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </p>
  <p>
    <%= f.submit 'Create' %>
  </p>
<% end %>

<%= link_to 'Back', articles_path %>

Because when I run my Cucumber scenario, I get this:

Scenario: Create Valid Article                            # features/article.feature:16
  Given I have no articles                                # features/step_definitions /article_steps.rb:8
  And I am on the list of articles                        # features/step_definitions/webrat_steps.rb:6
/home/deploy/www/www.trackingplace.com/app/ccc/app/views/articles/new.html.erb:3: warning: multiple values for a block parameter (0 for 1)
from /usr/local/lib/ruby/gems/1.8/gems/actionpack-2.3.3/lib/action_view/helpers/capture_helper.rb:36
When I follow "New Article"                             # features/step_definitions/webrat_steps.rb:18
  You have a nil object when you didn't expect it!
  The error occurred while evaluating nil.error_messages (ActionView::TemplateError)
  features/article.feature:19:in `When I follow "New Article"'

But I don't understand the error, or how to fix it.