I've never done this before, so don't trust my word completely.
1. If you import a sprite sheet into Flash by choosing Archive > Import > Import image, you should get your sprites all lined up as the creators did them. Mark the whole thing, then move your mouse up to Modify > Bitmap > Trace Bitmap. You'll then need the following settings:
Color treshold: 1
Minimum area: 1
Curve fit: Pixels
Corner treshold: Few corners (not sure on this one)
All of your sprites will then set to the .fla document. Mark the background and delete it, if the thing isn't transparant. Now, you can make new symbols and copy your sprites into the frames to get your sprites moving. Remember to use movie clips inside graphics a lot, as it will help during animation. If you for example make Link, he will be one symbol with all of his motions inside.
2. If you import a gif by going to Archive > Import > Import movie, then a number of frames will appear in the timeline. You then already have the movements ready, and all you have to do is to fix the symbol.
Flash is exciting!
