Hey guys, this isn't all that hard, but I wouldn't recommend this for beginners.

Materials:
The actual copy of game (Used for tricking the Xbox)
An open Xbox 360
A modded copy of the game (Call of Duty: World at War)

I am going to give you the step-by-step instructions, and if you have any questions or concerns then send me a message or reply to this.

1.) You need to take the Xbox apart (Yes this WILL void the warranty, but the warranty does nothing at all)
2.) When you get to the disc drive, take off the top, there will be a circular shape which you will have to cut out because you need the magnet inside, I repeat YOU WILL NEED THE MAGNET.
3.) Now that your Xbox is opened you will need to put the game in (Like WaW for example) and then place the magnet down so the disc doesn't fly out.
4.) You will be able to see the laser "checking" the disc, as it is doing that, press 'Y' to view game details, then scroll down to "Install Game" so you can wait.
5.) When the laser isn't seen anymore, that is when you will press 'A' to "Install game", but as it starts up take off the magnet and replace the real copy of the game with the modded copy then place the magnet back on.
6.) Hopefully it will be installing the game to your hard drive, if it doesn't, then repeat the steps.

My GT on Xbox is xTurtle Sauce so add me.

Once I get a new copy of WaW I will be hosting lobbies.

Hope this tutorial helps!