At the moment you'd need to use Poser to add the posability to your figure (and you'd need to make sure you set the model up with goups foe each part you want to move). We all hope there will be rigging tools for D|S, but nothing has been said about when (or if) they will appear. You'll probably never be able to load figure animations into Bryce 5.5 - it doesn't support the features needed for joints to work. It is a popular feature request for a future version, but I don't think anything has been said about whether it could appear in bryce 6, or later, or at all.