I don't think it will do as well as Halo 2 because of the incredible hype of other games this year, the lower install base (chart halo2 around week 150?, halo 3 around week 93?), RROD and Disc drive problems may inflate the installed number (I never got mine fixed, I traded it in for my Wii, before warranty extensions),
Guess: Halo 3 will get mediocre reviews and less word of mouth than 2, cutting off its legs. GoW, Bioshock, etc. will be competing. But really, who knows?
I am surprised at the lowish attach rate of Halo 2. Halo 2 was by far one of the most solid experiences of gameplay, graphics, and fun on Xbox. I would think more than half would have a copy, could this be from piracy, rentals, Xbox owners who bought it for Zapper.
Edit: Fixed link.
I would cite regulation, but I know you will simply ignore it.
