Well, just like Yahoo! Groups, you need an account. But for those PC users, you don't need to worry.
From http://www.mac.com/1/Groups_faq.html
引言回覆:
PC users can create a .Mac ID (and get a free trial membership) just the way Mac users can. The .Mac ID is theirs to keep and use for .Mac groups, AIM and iChat chats, the iTunes Music Store, and the Apple Store, even if they don't join .Mac when their trial memberships expire. PC users will be able to view and create group web pages, send and receive messages, and view the group calendar. Some PC users with software that has support for webcal protocol or webcal://URL can also subscribe to the group calendar.
It's free to join, and you can keep using the .Mac ID after the free trial period.
Free .Mac ID can be used for AIM
