I have Vista and voice chat works just fine in Yahoo Chat, although there is a patch for it that you can search Google for. I don't know which site to get it from though, because I never needed it. And only certain rooms are FULL of bots, most of the other ones (politics, games, books, music, etc.) have SOME bots and then mostly humans.
I don't know of any other chatrooms though, because I don't use them. Sorry.