Instructions
Turn on your Xbox 360 and go to ̶0;Family Settings̶1; option in the Xbox 360 Dashboard. You will find this under the ̶0;Settings̶1; tab in the ̶0;My Xbox̶1; menu on the main dashboard.
Ensure that family settings are disabled, particularly the ̶0;Original Xbox Online Games̶1; option. If this is enabled, it will prevent you from logging in to Xbox Live in "Halo 2."
Log in to Xbox Live. From the 360 Dashboard, press the ̶0;Xbox̶1; button on your controller, go to ̶0;Sign In,̶1; and sign in to an Xbox Live Gold account. Only Gold accounts can play games on Xbox Live.
Insert the "Halo 2" disc into your Xbox 360. Once the game loads, you will be prompted to download an update to enable play for this original Xbox game. Once the update is installed, the game will automatically restart.
Select ̶0;Xbox Live̶1; from the "Halo 2" main menu to start your online game.