When modeling in 3d, typically you'll use an image as a template. But what about animating in 3d? Blender can use a movie as a background. Just import the movie in the same manner as a background image:
Select View->Background Image...
Click Use Background Image
Select your movie from the File Browser
When it loads, click Auto Refresh. I had to move my Background Image window to get it to show the loaded movie.
Clicking Auto Refresh is important as that advances the movie when you advance frames in Blender's Timeline.