I put together a simple example of a nested form using Rails 2.3. It
shows a traditional master-detail form (an order with line items, in
this case). It uses two simple AJAX helpers to add and remove child
records.
The code is here: http://github.com/canonical/OrderItemsExample
An explanation is here: http://joemcglynn.wordpress.com/2009/11/24/the-canonical-project/
Joe