Halo 2 is comming out for PC soon, on Vista.
you dont need to know the story really... At tne end of halo 2, we are basicly in the same place as the end of halo 1..
we Arive back to earth, Only to find the Covenant attacking.
two main Difrences, Your on some Forunner ship, and Cortana is stuck on the last halo you where on.
( also, a small groop of Elites is probably going to Defect and join the Human side )