Unlock it where? It's already in it by default.
Unlock what head?
get all the skulls easily u can you tube it also u can play multiplayer online to unlock items getting halo ODST u can unlock recon by doing the vidmaster challenges in halo odst and halo 3
You unlock the armor.
you have to complete halo 3 odst on legendary, have xbox live and complete halo 3 on legendary
There isn't a known cheat code for this on Halo 3.
rocket launcher, pod rocket, or flamethrower... depending on personal preferences.
Your work for them.
No
Unlock Halo 3:ODST's Campaign Complete Achievement. Once you beat the ODST campaign, visit Halo Waypoint on the dashboard to unlock the item.
for finishing the halo 3 campaign on heroic you unlock the E.V.A helmet, plus the shoulders and body plate for certain missions.
All in halo 3 and all in Halo 3 ODST.
go to http://hubpages.com/hub/Halo-3-Armor