Well if you have two live accounts on you could both get armour. For example barry067 and simon4539 you could both get armour on the same xbox and play online with it. Weras if your playing as a guest then you can't because they don't gain xp.
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
In Halo 2, Master Chief has Mark VI armor which is an upgraded version of the Mark V armor from Halo 1. If you're looking for the reason why his armor had changed between Halo 2 & 3, I think they just upgraded it, but not enough to call it Mark VII armor.
There is no Brute armor in Halo 3, only Elite and Spartan models.
go to http://hubpages.com/hub/Halo-3-Armor
yes you still unlock the armor. you and the player that your playing with unlock the armor. =] =) =p q=].
you get all the vidmaster achievements on halo 3 and halo 3 odst
NO
Mark IV is a type of armor in the game: Halo 3. This is a evolvement from the Mark V armor in the previous Halo games; Halo:Combat Evolved and Halo 2. The armor is also called the Mark 6. In the game it is an armor that is worn by the main charecter: Master Chief. In the multiplayer game it is an armor that you automaticaly wear in the matches.(there are other armors to wear during matches)
recon armor
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3
there is no permanent cheats in halo 3. you need to unlock them by achievments. and, you can not get the flaming armor effect, it is only for bungie employees. in halo reach, buy the legendary package to get that armor effect.