how do u unlock the helmets on halo 3?

[Mike]

i dont care about the rest, but can someone give me a list of helmets and how to unock them?
i think i have the EVA, CQB, rogue, mark V and VI.

 

[WHITNEY05]

You need to unlock the skulls, first...

To find the skulls you can check out this page:
http://hubpages.com/_2eak79825f5lz/hub/Halo-3-Skulls

 

[Jas]

if you want to unlock all the helments and other amom when playing online multiplayer your have to collect all the skulls