Form Posts Across Different Controllers?

I have a basic, basic question about form posting across different
controllers. I think I'm having a fundamental problem understanding html
forms, while ruby I understand fairly well.

If I have on my "item" "show" page:

<% form_tag '/users' do %>
  <%= hidden_field_tag "id", %>
  <%= submit_tag "Add Item" %>
<% end %>

and in my "users" "show" controller I have:

def show
flash[:notice] = params

I just want some sign that my items controller has passed an id in the
hash to the users controller. For some reason this does not work and
only "actionshowcontrollerusers" shows up in the hash. If I could just
get the item ID from the items controller, I'd be set, but for some
reason I'm not able to transfer data between controllers...

PLEASE help. Thank you.