Only if you start a custom game and invite friends, but not online like a matchmaking match.
You can't. The Mythic Maps our only playable on Halo 3, not Halo Wars.
Yes, in a way. Halo Custom Edition has most of the features that Halo Combat Evolved has, except the custom edition is made only for online-play, and in the multiplayer setting, people can design their own maps with certain programs and play in the user-created maps with the whole Halo community.
well I am not sure what you are asking but I will answer both ways. option 1:No you can not play all ORIGINAL halo maps, but you can download them from file share. option 2: yes you can play all maps from the start of the game!
yes and no. You can play all the maps in the halo 3, but you have to download the rest.
play sonic in halo just download and the maps change
MAPS
If by "halo 3 maps" you mean the Halo 3 Heroic, Legendary, Mythic and Cold Storage maps, then yes. However to play campaign levels, you must actually advance in the game to get to them.
Its only the HALO:CE maps
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.
halo 3 ODST will probably come with a second disc with all the Halo 3 Online maps on it (all 21) plus 3 more. will be halo 3 format.
Halo Zero cannot be played online. It must be downloaded from its website and installed. It does not support online play in the campaign, being a sidescrolling shooter game, but it does have several multiplayer maps.
with a 360 NO. but you can play halo 2 on PC for free