First you have to be on the side with the MP40, then you open the stairs, don't open anything else on that side.

It doesn't matter about the other side, then you kill yourself by the wall by the stairs, tell the other guy not to revive you.

Next round get in the corner of the double tap machine and tell the other guy to watch the window.

Everybody else to get somewhere behind the machine, if anyone gets in front of the machine the zombies will get out from the corner and start running to you.

If you are the one in the corner of the machine and you get down then they will start running towards you.