Defeating the Ghosts
Here's how to defeat all the ghosts.
Fatso near kitchen (feed him hamburgers)
Stinky (spray perfume on him)
Stretch (use glue)
Fatso in bathtub (use camera)
General Fatso (use wind up key then hammer the tanks)
Farmer Stinky (use hammer and chisel to carve the stone in Caspers Image)
Graveyard Stretch (Use twister morph to lure him into grave dig site)
Drift
Go to the topleft corner of any room. Press and hold : (up + left) + L1 + R1 + Start. If done correctly, the game should freeze. Then release (up + left) and L1. While still holding R1 + start, press (down + right) and then press triangle. The game should then unfreeze and you should have the ability to drift over any wall by pressing R1. The L1 button will bring you back down.
Secret Room
On level one, go all the way up the stairs and turn left, then use the "Drift" cheat and drift over the walls and go down. There is a secret room.
Turbo
To make Casper travel faster than a speeding bullet, press triangle+X, R1, R1, R1 at any point during play (whilst accessing this cheat you will be transported to the inventory screen).