Microsoft reports via the Gamerscore Blog that the lucky few who manage to get their mitts on an early copy of Halo 3 won't be banned from Live for giving it a spin:

If you obtain a copy of Halo 3 prior to its street date of Sept 25th, you will NOT be banned from Xbox Live for playing Halo 3 early (not even my fellow softies).

So how does one obtain an early copy of Halo 3? I hear that there is a magical gnome that lives at the base of a tree in Topeka, Kansas that will give you a copy if you bring him the blood of a unicorn. Other than that, I have no clue.

Hmm...by "gnome" do you think they could mean "corrupt Gamestop employee" and by "blood of a unicorn" could they mean "a few hundred dollar bills"? You decide.