This shot is clearly from the MWNY '99 vintage, as evidenced by the different interior textures and the early Elite model, with dramatically different facial features; only the general shape and the legs are similar to what the Elite eventually became.

The original press release for Halo mentioned an array of weapons from "composite swords" to "orbital bombardment". Neither made it into the shipping game. Note the complex scene with several characters and vehicles in the background. When Halo was still imagined to be a third-person perspective game, it would have been possible for scenes like this to appear during gameplay.

Like several other models, the Pelican here is easily recognizable, despite coming from an older build of Halo.

Another shot of the Master Chief in front of an early tank model. Difficult to say whether this is the Scorpion or the Stealth Tank, but from the coloration I'd guess it's the Scorpion.

Beams from this Covie's weapons are a slightly different color than we're used to-- not to mention the use of continuous streams rather than discrete bolts.

The marine, Master Chief and Warthog models are all seen here in their E3 2000 form, very close to the eventual final versions.

Although this screenshot was taken before Halo's engine was changed to suit the Xbox, the Hunter model seems clearly very close to its final form.

The famous E3 2000 demo featured the revised, chunkier Master Chief model, which was controversial at the time-- and a dramatic script and fantastic visuals that made it instantly popular. It was shown to an audience of fans at a Bungie FanFest at Neutral Ground in New York, New York, scheduled to coincide with MacWorld that year.