Updating scaffolding form field

This may be a basic question, but i have an “image” field in a “news”
table, and have a form that uploads the image. Following the upload,
the “new” action is called in the rails scaffolding so i can add the
rest of the news to db entry. I however want the “image” field to
contain the image “id” that was just created in my image table. I send
the value to the new action, but cannot get the field to default to
this value. As i am fairly unfamiliar with where the scaffolding is
storing the information for this form I am having trouble figuring
this out. I am unable to find the _form teplate as is described in
pickaxe as a partial. Here is the code for the view. The second form
is the form I am using to upload the image. So my question is how do i
get the image field to use a default value that was passed to the view
rather than what is stored as default in my db.

New news

<%= start_form_tag :action => ‘create’ %>
<%= render :partial => ‘form’%>
<%= submit_tag “Create” %>

<%= end_form_tag %>

<%= form_tag({:action=>‘save_picture’}, :multipart => true)%>

<%= link_to ‘Back’, :action => ‘list’ %>