Mikey,
Actually, yes. I download a sprite sheet from Spriters Resource online. Then I edit them in a graphic program. I seperate the different pieces like any typical puppet animation.
Then I double the size four times while preserving the hard edges. After that, all I do is import them.
If your actually interested in doing sprite animation, I highly recommend the following two programs.
Alferd Spritesheet unpacker. This program will seperate all the sprites in a sprite sheet for you into seperate images within 10 seconds.
AnyPic Image Resizer. This program will double the size of your sprites multiple times so they are ready for import into AS.