I'm wondering this as well, that thread doesn't really give me the info I'm looking for though. Are there requirements? Paper work? Do you have to be NPIP?
Their regulations are available online or you can go to your local post office and get a written copy there. Now, that's only information on shipping chickens; it won't cover licenses or other local requirements/restrictions on the sale of poultry. If you need that sort of information, I'd start with your local extension.