Before Halo 1 it the first and last.
Halo Reach is essenetially Halo 4, but it is based before Halo CE (Halo 1). It is due to come out in Autumn (Fall) 2010. The beta is a multiplayer test of the game by owners of Halo 3: ODST and will begin on 3rd May 2010. There were also similar beta tests for Halo 2 and Halo 3. Halo 3 beta contained only matchmaking and 3 maps: Highground, Snowbound and Valhalla. Thus I expect the Halo Reach beta to be similar.
halo 3 obviously
Halo 3: ODST is the newest of the two, but not the newest Halo game.
The halo time line goes Halo Wars, Halo: Reach, Halo:CE (halo 1), Halo 2, Halo: ODST, Halo 3. Halo 3 and ODST are practically at the same time.
After Halo 3 there was halo wars, halo 3 ODST, and Halo reach. A new company (not Bungie) will be making a Halo 4 and rumor has it there will be a remake of Halo Combat Evolved.
Halo 3 ODST is not for PC but Halo 1 and maybe Halo 2-3 are
it goes halo, halo 2, halo 3, halo 3 odst and soon halo reach will be available
Halo Games: 1. Halo: Combat Evolved (Xbox, PC) 2. Halo 2 (Xbox, PC) 3. Halo 2 Muliplayer Map Pack (Xbox) 4. Halo Triple Pack (Xbox) 5. Halo 3 (Xbox 360) 6. Halo 3 O.D.S.T (Xbox 360) 7. Halo reach (Xbox 30) Other Halo Games: 1. Halo Zero (PC) 2. Halo: Custom Edition (PC) Future Games: 1. Halo Wars (Xbox 360) 2. Halo: Chronicles (Xbox 360) 3. Halo 3: Recon (Xbox 360)4. Halo 3: ODST (Xbox 360)
The names of all the Halo games are (in order): Halo: Combat Evolved, Halo 2, Halo 3, Halo Wars, Halo 3 ODST, Halo Reach, Halo: Combat Evolved Anniversary, and Halo 4. In chronological order: Halo: Wars Halo: Reach Halo: Combat Evolved/Anniversary Halo 2 Halo 3: ODST Halo 3 Halo 4
in HALO 3 you are a Spartan and in HALO 3 ODST you are a Orbital Drop Strike Trooper (ODST)
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3