! Here i got this sweet thing off halo2.com that will explain everything for you:
HALO THINGY FROM HALO2.COM!
The epic saga continues with "Halo 2," the much anticipated sequel to the highly successful and critically acclaimed game "Halo: Combat Evolved." In this sequel, the battle comes to Earth, and Master Chief, a genetically enhanced super soldier, is the only thing standing between the relentless alien Covenant and the destruction of all humankind.
Pushing the Xbox hardware to its very limits, "Halo 2" will expand on everything that made the original game great, plus add a wealth of technological and gameplay advances. Significantly improved graphics, enhanced AI, destructible and interactive environments, and an advanced real-time lighting engine are just a small part of Halo 2’s evolution of design and technology. Every improvement in Halo 2 is designed to take gameplay to a new level, and in the end, to tell a better story.
The closely guarded plotline of "Halo 2" will feature new vehicles, new weapons and new environments as well as new enemies, allies and surprises around every corner. Players will wield dual weapons, board opponents’ vehicles, and in multiplayer mode you can even switch sides and take the role of a Covenant Elite.
Working in concert with Xbox Live to redefine broadband gameplay, Halo 2 delivers superior online multiplayer action. Whether joining your lan on a new multiplayer map, customizing the look of your armor, or checking player stats in-game and on Bungie.net, Halo 2 will bring Halo’s unique social experience to a higher level with Xbox Live.
Released in November 2001, "Halo: Combat Evolved" became recognized as one of the greatest achievements in video game entertainment. To date, "Halo" has sold more than 4 million copies worldwide and continues to be a top-selling title.
Cause other wise it could be a while before i get a copy. 
