How do I unlock skins in Halo 3?

[Lipiew]

i've seen screen shots of different mast chiefs from Halo 3 and i was wondering how would I unlock them?

 

[apegonehobo]

E=Elite
S=Spartan


(E) Ascetic Body Unlock "Up Close and Personal" Achievement
(E) Ascetic Head Unlock "Steppin' Razor" Achievement
(E) Ascetic Shoulders Unlock "Overkill" Achievement
(E) Commando Body Unlock "Triple Kill" Achievement
(E) Commando Head Unlock "Overkill" Achievement
(E) Commando Shoulders Unlock "Killing Frenzy" Achievement
(E) Flight Body Complete Tsavo Highway On Herioic or Legendary
(E) Flight Head Complete Campaign mode on Heroic difficulty.
(E) Flight Shoulders Complete The Ark on Heroic difficulty or higher.
(S) EOD Body Complete Tsavo Highway on Legendary
(S) EOD Head Complete Campaign mode on Legendary Difficulty
(S) EOD Shoulders Complete The Ark on Legendary difficulty
(S) EVA Body Complete Tsavo Highway on Normal or higher
(S) EVA Head Complete Campaign mode on Normal
(S) EVA Shoulders Complete The Ark on Normal difficulty or higher.
(S) Hayabusa Chest Collect 5 hidden skulls
(S) Hayabusa Helmet Collect 13 hidden skulls
(S) Hayabusa Shoulders Collect 9 hidden skulls
(S) Mark V Head Unlock "UNSC Spartan" Achievement
(S) ODST Head Unlock "Spartan Graduate" Achievement
(S) Rogue Head Unlock "Spartan Officer" Achievement
(S) Scout Body Unlock "Too Close to the Sun" Achievement
(S) Scout Head Unlock "Used Car Salesman" Achievement
(S) Scout Shoulders Unlock "Mongoose Mowdown" Achievement
(S) Security Head Earn 1000 Gamerscore points.
(S) Security Shoulders Earn 850 Gamerscore points.