[quote name='DTJustice']I just ordered mine, I bought an XBOX this week, so I don't have any of the previous Halo's. If friends of mine have Halo 3, and I have 3 ODST, can we play multilayer together?[/QUOTE]
Yes, but ODST has all map packs while Halo 3 needs to buy the DLC map packs so unless your friend has all the maps, your choices in playlists/maps will be limited, but you'll still be able to play together.