Ok, its time to settle a long running misconception.  Final Fantasy: The Spirits Within is NOT, I repeat, NOT going to be based on any games from the Final Fantasy series. Furthermore, there are currently no plans to turn the movie storyline into a game.  The movie is an original story written by some of the Final Fantasy series' best writers and animated by the same CG animators that animate those gorgeous FMV cut sequences that are integrated (in some cases seemlessly) into the games.

For more details, check out the Final Fantasy: The Spirits Within webpage by Sony.

Now, I sincerely hope that I will stop seeing webpages that say that the movie is based on a game.  Although, i would love to see the Final Fantasy VII storyline turned into a full length feature film (HINT HINT WINK WINK NUDGE NUDGE all you Sony producers out there).