Here are the screenshots:
|(MCedit didn't work, so I was not able to set the spawn point. Just don't destroy the bed)|
You know that Zombie Flesh that Zombies drop? Well that is your money, to purchase anything you want. You throw it in the space beneath the dispenser -with a sign beneath it, so you can see whats in the dispenser- and the dispenser will shoot your stuff. You can repeat this many times, but the dispenser may get empty. When that happens, just break the glass and put some new stuff in it, if you have toomanyitems or such.
This is such a dispenser:
There is an hidden chest in (almost) every zombie spawn room. In those chests are levers. You have to put those levers on a gold block. That will open the gate to the next room.The door to the next room is most of time hidden. Good luck!