Essentially the process is the same for both:
- create your idea and a short script
- collect photos and audio files (media)
- import your media into the program editing area (stage?)
- add effects or animation, tweak the timing, add credits etc
- export the movie
In favour of powerpoint:
- teachers and students are more likely to already know the program
- you can add text to the screen much more easily (a mix of images and text can be useful for language learning)
- you have more options in your animations
In favour of movie maker: