You need to sign up for an account if you want to use the boards and chatroom, but you need to sign up for most chatrooms nowadays anyway. You don't need MSN Messenger or anything, it's just like signing up for Pet Talk.

But if you don't like that one, try

Cavies Galore

Practical Pet Care

Cavy Madness

Piggy Palace

Wheek All About It

Guinea Pigs World

Cavy Compendium

Some of those only have message boards, not chat rooms, but you can chat about your piggies and post pics, etc. so they look pretty good. Hope that helps