FreeSpace movie, huh? I hate to be a buzz-kill, but I have two words for you: Wing Commander.
I'm not so sure we want a FreeSpace movie. When you have a mammoth plot line that spans half a galaxy of space and months or years of time, it becomes extraordinarily difficult to cram something like that into a two to three hour chunk of time. There's simply no way to slice it, where something critical doesn't get left out. You can't grab the beginning and end of the Great War and expect a movie to make sense to movie-goers without the dozens of scenes in the middle. You can't pick up the fight for Capella mid-stride, and expect people to understand the first damn thing about what these unseen "NTF" fellows have to do with anything. Likewise, you can't start with the GTVA fighting Bosch, and end with the Iceni jumping into the nebula. (That'd be like ending a video game series with eighty Sathanas juggernauts detonating a star, with some jumping out in the process. Oopsy?)
If it had to be a movie, then I'd probably want to see as much of the NTF civil war as possible, from Admiral Bosch's perspective. He's a rather enigmatic character in the game*, and I'd like to see what went into developing him. It would also be an angle that most people who have played FreeSpace haven't seen, largely eliminating the "Well, I'll just play the game again and save eight bucks" factor. Furthermore, I've been tired of cliché 'happy' endings, wherein all in the world/galaxy is set right, for quite a while now, and the movie-watching public is beginning to follow suit. I don't care how happy Bosch says he is in his final log entry, his rebellion's cause has become polluted; his armada has been crushed; he's gotten lost in the nebula he's been exiled to, and there are reasonably good odds that he's about to be eviscerated by the beings he wants to call friends.
A movie may be impractical, but as some people have suggested, I think a television series would be doable. I'd guess that each game could be divided up into enough episodes to make two or three complete seasons. There's probably at least one or two more seasons riding on the coattails of the aforementioned juggernauts. As long as the writers could avoid silly developed-in-a-season romantic subplots, I'd want to see such a television series focus on the pilots, but not the Alpha 1 god-pilots. Some of my favorite parts of FS2 are in the early and mid sections of the campaign, where you really feel like just another cog in the military machine, which is what they are. When you achieve official uber-l33t status in the game, the whole atmosphere changes from one of, "You're another cog in the machine," to, "You are THE cog in the machine!!!"
Of course, the hardest part of a FreeSpace television series would be the transition from the Great War to the events of FreeSpace 2. Simply popping text up on the screen in the first episode of season 4 saying, "Thirty-two years later..." would be especially lame, especially since you're totally rotating out the old cast. The show might almost need an extended hiatus and come back with a snappy, new name, like FreeSpace: The Next Generation. Oh... Right... Already been done, eh?
In summary, either game alone and certainly both games together would be too much for a movie. As a series, it could be done, but without a good team of writers, it could also turn into six different kinds of crap.
* -- His four monologues establish that Bosch has a great deal of depth, but you have to admit, it's not fully explored.