I saw someone post something like this not too long ago, and I thought I'd try and go one better by trying to get all the Halo 3 achievements in 13 days, before Reach comes out. I started yesterday and completed the campaign on legendary in one day and today I got all the skulls and terminals. I've now got to do campaign scoring, the three vidmasters, and multiplayer, and then I'm done. I will keep this thread updated with how I get on.