I just got Halo 3 ODST, but i don't know how to play the maps that aren't just on

[derexboulder]

halo 3? I'm just confused, whenever i go into social slayer i just get stuck playing the normal maps from halo 3. how do i play the other like 20 or so maps that are the DLC maps and the unique ones from halo 3 odst. Any help will be appreciated.
-Thanks

 

[Rasputin]

If you were looking for multiplayer you should just return it and get gears 2

 

[Duncan]

there are no new maps in the multiplayer one if u put in your odst one and play firefight there is a bunch of new maps