For the customized pets' dialogue, you have to edit the pettalktable in your grf which isn't too hard to edit. However, even without editing it, my pets still talk (but as a poporing or some other old pet messages).
Yeah, for the new taming items, you have to script them or find the scripts on Eathena. They have *some* working pet scripts there though there are still a few errors with some new pets. They have some MvP pets and such included.