all of them i believe
Yes, you do.
yes
Go to game marketplace, go to game add-ons and look for Halo Reach. You need to be with Xbox live if your not.
Yes you do because whats the point having all the maps and then you play them on your own. Plus you need online to download the maps.
There is no Halo 3 mod for Halo Trial. Halo Trial is one of the hardest versions of Halo to mod. There are however, custom maps for Halo Custom Edition. To get Halo Custom Edition, you need to have Halo: Combat Evolved installed on your PC, you also need your CD key. You can download Halo: Custom Edition free.
I would ask of you to be more specific, but since its not possible to change your answer, I'll say both. To get Forge maps, make an account at http://www.bungie.net/ (I did not need to copy and paste :-P) and download directly to your XBox360, then start a local game and it should say Download Complete. To get map packs, go to the market place, look for the tab that says "Map Packs" and find the Halo 3 Map Pack you want, then it should download, and then you'll have the maps in Halo 3.
you need to download the heroic map pack with 3 maps.......... foundry, rats nest, and standoff and there is the legendary map pack with 3 maps also..........avalanche, ghost town and blackout and the new mythic map pack with 3 maps.........orbital,sandbox and assembelly*
You can do it with a Silver account (now simply known as Xbox Live Free), but you will still need a Gold account to play those maps in online multiplayer.
You need to do forge to create your maps in halo 3
if you mean to "unlock" them...no. You have to purchase and download those maps. They simply arent on the game disc and need to be installed on the hard drive. You also could buy ODST, and that includes a second game disc that has everything Halo 3: Multiplayer on it.<-----thats they best deal, plus you get Halo: Reach multiplayer beta
If you are referring to the Firefight maps they open as you campaign.
You can't, you need Xbox Live