Where do you get the Fire Medal, Ice Medal, and Water Medal?

Fire Medal: In the Mirror Room
When you enter this room, a fence will cover the door locking you in. There is a huge mirror on the wall.

The ghosts that attack you will be invisible! You have to use the mirror to see them. After sucking up the ghosts - a chest will appear. Open the chest to reveal the Fire Medal.

Now go to the pillars with the embers on them and an element will come out. Suck it up to gain fire. Now notice the candles around the room. Set them aflame and the fence over the door will disappear. Leave.

Water Medal: In the Kitchen
First notice the burning door. Now what are you going to do? Remember there is a random golden mouse in here. Okay - first suck up all of the flying dishes and pans.

Then search the oven for a money ghost. Then search the other oven and you will see a roast or something on a pan. Flame it and a red gem will fly out!

Open the freezer to the left of the oven and an ice elemental ghost will pop out. Flame it and then suck it up. The lights will come on and a chest will appear. Open it to obtain the Water Medal.

Go over to the running faucet and a water element will fly out. Suck that up and search the cupboard for money. Check the light hanging from the ceiling for money. Then go to the burning door and cool it off with the water. Go through the door.

Ice Medal: In the Tea Room
Suck up all of the flying silverware. Then search the cabinets for money and a red gem. Go behind the table and you will find a gold mouse. There is also a random mouse in here.

Suck up all the ghosts and a chest will appear on the table. Unfortunately - for some strange reason - Luigi can't jump. So go step on the warp pad. You will be sent to the ceiling!

Suck on the chandelier for money and then step on another warp pad to fall on to the table. Open the chest for the Ice Medal. Go to the bucket and an ice element will come out. Suck it up.

Now you can leave.