XBox demo boxes had problems for one of two reasons : inadequate cooling (which isn't good because the "demo" boxes are actual production boxes) and bad game code. Most of the Halo CDs were shipped with unstable versions of the game (video driver conflicts). Microsoft denies both problems, Bungie (maker of Halo) specifically cites Microsoft as shipping the wrong version of Halo for demo use that's causing their game to lock up.
Halo was never meant for the XBox, it was meant for a real gaming machine (the one you're sitting at right now). No first person shooter has ever not sucked for a gaming console minus GoldenEye for the N64 because you used all of two buttons. Halo was dumbed down significantly in terms of gameplay in order to make it playable ... which inherently made the game suck. I think they'll have to release Halo for the PC just to make up for the complete suckage that it will be on the XBox.
Get a PS2, play Gran Tourismo 3's Rally Racing until your fingers fall off. I'd consider a GameCube, but I don't want to play Pokemon...