http://halo.wikia.com/wiki/Armor_Permutations
look here.
There is no Brute armor in Halo 3, only Elite and Spartan models.
certain achievements give it to you
No, only elite's.
you will get elite flight armour
I assume you are asking if you can customize your Elite armor in Halo 3 multiplayer to include the katana? No you cannot.
All the armor are the same it's just the way how you want to look WRONG! the best armor in halo 3 is the recon armor and you have to be a member of bungie OR get all 7 vidmasters in halo 3 ODST
beating the campaigne on legendary is a fast way of unlocking most the armor. some achievemnets also unlocks armor.
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
go to http://hubpages.com/hub/Halo-3-Armor
you get all the vidmaster achievements on halo 3 and halo 3 odst
rmor Permutations are a feature in Halo 3, Halo 3: ODST, and Halo: Reach that enable players to customize their multiplayer character's armor to their liking. In Halo 3, this feature allows players to change the helmet, shoulder, chest pieces worn by their multiplayer character. In Halo 3: ODST, players can choose between the preset armor of their squad members, and can toggle whether or not their character wears a helmet, though this will not affect health. In Halo: Reach, players can purchase different armor from The Armory, which also includes wrist armor, knee guards, utilities, visor colors, and armor effects. Players also have the option of choosing between being a Spartan or Elite in Halo 2 and Halo 3, and can set a preference for either in Halo Reach.