If you're going to attempt anything like LotR in an Airsoft game, you've got to break it down into a very, very basic term set, and take away pretty well everything that makes it a fantasy. Then, you can build it back up, and reconstruct it into a more modern version of the same story.
The sparknotes website has a plot overview of the entire series. Using that as a guideline, we can then break down the essential story and build it up from there. First, we have an item of incredible power. Whatever it is, it has to provide some advantage to both the person using it, and the person seeking it.
In keeping as close to the story as possible, you'd have to have more than two, easily distinguishible groups. You've got Frodo and his entourage, a couple of kingdoms with "armies," and misc. squads of mercs.
Then, you've got the main characters, who each have their own agendas. Frodo's is to get the object deep into enemy territory to destroy it, and, in turn, the enemy's will to fight.
Samwise, Merry, and Pippin are there to protect Frodo, help him keep his sanity, and aid him in his quest. Sam is Frodo's personal bodygaurd. It is his duty to make sure that Frodo succesfully makes it to Mordor and destroys the ring.
Each of the others would have a mission, Aragorn to reclaim the throne and unite the kingdoms of Man, Legolas to aid Frodo as he sees fit, Gandalf to undo the controlling power Saruman has over select officials in control of potential allies to their cause, Gimli to be the wise-cracking, comic-relieving sidekick (sorry, Gimli), that sort of thing.
There will be mercenary troops that will aid whomever offers them the best payments (Perhaps in the form of promises or ammunition and supplies).
I might add more to the concept later. It's late, and I'm tired. Either way, I wouldn't actually call it Lord of the Rings. Something similar maybe.
P.S. My lvl 10 Angelic Dwarf with twin Mithril Great War Axes pwns all. Nevermind the fact that I had to bribe the DM. >.>...