Notorious peripherals maker Lik Sang is now promoting a device called the SmartJoy designed to allow gamers to use a mouse and keyboard instead of the usual controller to play games on an Xbox, including Halo. HBO pointed out some salient points about the item, and so has TeamXbox. Our take? While we were big supporters of the keyboard and mouse combo prior to Halo's release, we've now become so used to it that using WASD in front of the TV just wouldn't seem AOK.
As far as whether or not using a mouse and keyboard would give a player an advantage over those using gamepads, this post seems to indicate that Bungie may already have considered this and has a way to deal with it by limiting turn radius.