// create.js.erb
$("#add_item_form").replaceWith("<%= escape_javascript(render(:partial => 'designs/items_form')) %>");


// application.js
jQuery.fn.submitAjaxItemForm = function() {
  this.submit(function() {
    $.post(this.action, $(this).serialize(), null, "script");
    return false;
  })
  return this;
};

$(document).ready(function() {
  $("#add_item_form").submitAjaxItemForm();
});


// designs/_items_form.html.erb
<% form_for [@design, @design_component], :html => {:id => "add_item_form" } do |f| %>
  <% unless @item_container.blank? -%>
    <p class="options-choose" id="item_container_label"><%= @item_container.label %>:</p>
  <% end -%>
  <% @items.each_with_index do |item, i| -%>
    <% line = i % 2 == 1 ? "odd" : "even" -%>
    <% content_tag :p, :class => line do %>
      <%= radio_button 'design_component', 'item_id', item.id %>
      <%= item.label %>
    <% end -%>
  <% end %>
  <%= submit_tag "Next" %>
  <p class="options-choose" id="ajax_msg">&nbsp;</p>
<% end %>