attachment_fu: I just want an attachment

Take a look at this, a small helper I wrote for exactly this task,
describtion in the rdoc:
http://pastie.caboo.se/132853

put it in lib/has_image.rb and then write your model

class Product < ActiveRecord::Base
  belongs_to :image
  include HasImage
  ...
end

Forgot to mention, this assumes your image model is called "Image".
Adjust the code accordingly if your Model is named differently