Resizing....I hate to even ask such a seemingly simple Q

I can’t for life of me figure out the following:

I have been given a new movie to work with that is 550x400
and I need to convert the movie to 578x291. The movie, in its original size appears in the middle of the stage and all I want to do is resize the stage AND keep the movie in the center.

How do I do resize the stage and keep the movie in its current orientation in relation to the stage without having moving every object, layer, motion guide, symbol by hand?

Thanks in advance.

B. Huston