Oh, and acid, don't forget to make the key an animated tile. it should look like this:
Key - Nothing - Key
Then with a trigger scenery ontop of it, and a trigger zone with on/off turned to 1(or 0 if you are turning it off), and the ID's set to the same, then when you go to get the key it should disappear. If you also want it to open a door, make a similar animated tile (Only with the door/blocks instead of the key) and place trigger scenery with the same ID on it. TOOODAAAA:-D