You must earn 1000gamer points from Halo 3 (on it's own) this will also get you the Katana. So basically just try and get all the achievements, completing the game on all the difficulties is a good start.
You have to get 1,000 gamer score on Halo 3.
Unlock all 49 achievements
To get the security helmet you need to have over 1000 gamer scorer from halo and 50 achievements.
No all 1000 need to be on halo 3
Depends on your definition of cool. It is an opinion.
Eva helmet, left shoulder security, right shoulder marksman, chest grenadier
There is no hayabusa helmet in halo reach
The halo helmet replicas are available in the following stores online; Spartan Helmet Replicas-Halo, Halo reolicas and collectibles on eBay, and Formula 1 Online Store Collection.
he is spartan under his helmet has another helmet
the commando helmet
There's no code for the helmet.
In halo 3 you must get 950 Gamerscore.