After looking at a link that xxshadowxx provided in an earlier thread about the H3 script...a lot of interesting information was on there.
Alot of this appears to be taken from the Halo2 DVD that came w/ the limited edition case. If half of it is true then it would be a very intense game.
There will be different variations of the Warthog, but I am unclear as to which. Possibly the Snowhog and the Transport Hog that were both removed from Halo 2.
There will be a human flying vehicle that has a similar design to the Warthog.
There will be a new Covenant vehicle, that will most likely be a replacement for the Spectre.
There will be a Forerunner flying vehicle, the Leviathan.
In the campaign, you can fly the Phantom.
In the campaign, you can fly the Longsword Fighter (the ship Master Chief gets in at the end of Halo: Combat Evolved).
As far as I am aware, all the other vehicles will return.
All the returning weapons from Halo: Combat Evolved and Halo 2 are being completely redesigned to fit into the game.
There is a weapon very similar to a SAW, or the turret on the back of the typical Warthog. It is held over the players shoulder and appears at the top right of the screen rather than the bottom right. It is very powerful, and whilst firing, you can see the bullet chain hanging down and going into the gun.
The Plasma Pistol is nothing like its Halo: Combat Evolved and Halo 2 counterparts. The charge-burst homing ability has been greatly decreased and it fires more like the Magnum.
There is a Forerunner staff-like weapon that emits a very powerful beam of light.
The Jackal Shield can be dual-wielded in both the campaign and in the multiplayer.
The Flamethrower can be used in the campaign.
In the campaign, the Forerunners use simple weapons that have the firing magnitude of the Scarab's cannon. If you've found the Scarab Plasma Rifle on Outskirts in Halo 2, you'll know what to expect.
The SMG will remain as the standard 'usual' weapon.
You will not be able to dual wield Energy Swords.
For more info visit - http://www.freewebs.com/jaxx931/halo3.htm