You do not start off as a rank because there is no online matchmaking for ODST
halo3 odst is an expansion of halo3 the only big difference is that you no longer play as a Spartan you play as an odst.
When you buy ODST it comes with a halo 3 matchmaking disc called mythic, it comes with the helm. Start> right stick tap right>apperance>armour> Helmet> ODST
no it will not it will have firefight like a halo version of gears of war 2 horde mode
no, just as arbitor and master chief.
If you install it onto your harddrive and insert the original halo 3 disk you can access the three extra maps and the matchmaking features.
You get XP by winning matches in matchmaking. If you lose the match, then you lose XP. Simple.
in HALO 3 you are a Spartan and in HALO 3 ODST you are a Orbital Drop Strike Trooper (ODST)
As far as I know, you can't because their isn't any online Option in Halo 3 ODST; Campaign Disk, BUT if you were to use the Multiplayer disk, you can get online/matchmaking, and play online, and get anywhere between 1 and 3 exp for games.
I would say Halo 3 ODST
Halo 3 ODST is not for PC but Halo 1 and maybe Halo 2-3 are
Halo 3: ODST is the newest of the two, but not the newest Halo game.