Add File Download Widget to Post (similar to add_theme_support for image)

Im using the custom_post_type in WordPress 3.0 to attempt to make my own catalogue/brochure.

One feature i need is the ability to add file attachments to certain products, either by a custom field or preferably in a similar way to how this code works add_theme_support( ‘post-thumbnails’ )

Could anybody point me in the right direction for this one?

Thanks
Dan