Well, while I don't know any script loader off-hand, I don't think it would be too hard to assemble a basic script reader.
Personally, I would use yaml, xml, or some other markup language to define a series of movements, construct a loader to load and parse the file at the start of the game, and inject the parsed movements into whatever handles NPC movement logic upon creation of the NPC. I don't think this would work too well for complicated movements, but I can see it working well for a series of predefined movements.
Alternatively, you could take SpriteBatch's approach, and have movements hooked up like the draw operations are done.
What do you think of this?