Don't buy this game, you won't be able to play it
I don't know why, but the game considers product keys from new, sealed copies to be invalid. I've tried three different copies from Amazon, and none of them work. I've seen threads about it on various Microsoft help sites, and the official response is always to call a phone number for Games for Windows support. Unfortunately, that number now redirects to support for Windows and Microsoft Office. I tried calling myself and was told that support has ended for Halo 2 Vista and there's nothing they can do for me.