Answer:
1. First, you have to download Vuze (a torrent client, as you will be using torrent files).
2. Then, go to extratorrent.com, or isohunt.com, and search for your movie. the more seeds and less leechers, the faster the download. Look for .m4v, .mp4, and .mkv files, because I know that Vuze can convert those to iTunes. I'm not sure about others, like .iso, etc.
3. Once the .torrent file has downloaded (it's very small, and shouldn't take long), open it with Vuze, and it will start downloading.
4. Now, once you have downloaded the movie, drag the main file to the iTunes tab on Vuze under devices, and it should start to convert it. this will usually take 1-2 hrs.
5. Once the video's finished converting, it should be in the movies tab in iTunes. If the status bar says 100%, you can delete the original video file. if the status bar says N/A, however, don't delete it, or iTunes won't be able to play the movie.
6. Put it on your iDevice and enjoy!