KoRnDawwg
-is writing an album
It has actually been reported that the Halo 3 programming is causing a lot of problems including lockups, disk-read errors and even the Red Ring of Death on a lot of Xbox360 consoles. It seems that it is definitely just the disk and it has occured on the standard edition of the game, not just the Limited and Collector's edition bundles. So as a result, I would not even touch the game with a barge pole if I were you. And that is the best advice I can possibly give if you are thinking of buying the game. Here is the link, but not the official source:
http://www.n4g.com/xbox360/News-70753.aspx
http://www.n4g.com/xbox360/News-70753.aspx