its easy u need 2 people to do it one person is in zombies lobby the other multiplayer the guy in zombies inv u u accept then wait a min and it will take u bck to the press start menu press start and quickley go to multiplayer then once multiplayer has loaded quickly go to system link and wait for an error to pop up and go to system link and buy wat ever classervied gun u want u can only buy guns and u have to have 2000 cod points to do this glitch