How do I move photos from Gallery into iMovie.

iMovie can only import pictures and movies from the Photos app. You will either have to sync the photo through iTunes, or use another app such as PhotoSync to copy it to the iPad's Photos app.

The Gallery app is only a viewer. The photos are stored on the MobileMe site. There is no provision for downloading. You can visit your me.com site on a computer and download photos from the Gallery that way, and then sync it back to the iPad by other methods.