Play in Co-op mode.

When you and your partner have 2,000 points or more each, one of you open the help door.

Each buy a weapon from the mystery box( works best with MG42, Browning and ray gun).

One of you should still have 1000 points or more, so move the couch inside the help room.

When upstairs go inside the room that has the grenades and sawed-off shotgun, because the zombies can only come in two ways.

The one with the faster shooting gun watch the door and the other watch the window (guy at the window can help his partner with the door).