You have to buy it from the Xbox market place. It should be the heroic map pack. You must have Xbox live.
No.
score 15,000 or more points on crows nest with campaign scoring on
I think that the disc for halo 3 you have is scrated up, so you can't load the maps. A scratched disk wouldn't stop you from playing Rats Nest because it is a DLC so either Something happened while downloading or your hard drive is messed up.
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
Unlock it where? It's already in it by default.
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.
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.