We would have this contest open ONLY to members of ONE paticular website/forums. All that would be required is that a user submit their nick (and other contest info for shipping) in order to verify when selecting winners that they're actually a member of your site. Also we'd put in a referer script to help keep the entries coming from your site
We ask nothing in return. Only that some of your users will browse our site and perhaps add us to their bookmarks. Your users simply have to enter the contest...that's it. Your users in turn get a free DVD set.