Update 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. I have tried :locals => { :image => :id} to see if that
overrides the default value set in the partial. As i am fairly
unfamiliar with where the scaffolding is storing the information for
this form I am having trouble figuring this out. 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’ %>