Well basically, with CoD WAW and CoD 4 you can burn the entire game on a disc in ISO format and install it on your console.
With Xbox there are certain methods of doing this, via Hotswapping or if your disc drive is flashed, you can just play it like a normal game. If you don't know what those things are i suggest looking up ModdedWarfare on Youtube. He has done a great tutorial on this.
Its kind of an old trend. But the cool thing about using this method is you don't need a modded console. You need an original copy of the game and a burned copy with the mods. If you use the hotswapping method it involves opening up your console to switch the discs at a certain point to get your console to install the modded version.
It only works with WAW because Treyarch didn't exactly install modding checks on the game. You can only mod camo's on cod 4. But with WAW you can get menus on zombies. Not multiplayer mode. But zombies online and solo.