First use importFileInto (to import a w3d file) then use
cloneModelFromCastmember and cloneMotionFromCastmember (see Director Help for
commands use)
Yes, when you import other shockwave 3d file (.w3d) all motions are imported
too, then you have to copy (clone) from the source (imported) member to the
target member (both shockwave3d members).