There is a program called Natural Pose or Susanna that imports posers animations into Bryce. If you don't do those you can use Bryce to do it by selecting the part you wish to move, set the time scrubber to where you wish,move the part and set a keyframe. Bryce will fill in the in-between frames from the first postion to the next position. All this should be in the Bryce help files.