Uh, wasn't there another thread like this? And someone said you coulda just googled it. xD
I like talking about the ghosts, so I'll post something interesting anyways. BTW, they freaked me out when I first saw them, xD
Um...if you see the girl and the butler at night, then run around like a maniac in the room with the painting, you might be lucky enough to come across a Gengar. And you also need like a GBA game like FireRed or Emerald in the GBA slot. But it's way rare.
Sometimes the ghosts won't appear when you first enter their rooms, so just keep going in and out till they show up.
There are alotta rumors of why there are ghosts. The fire, the poisin, the antidote, the twins. Just google it, and you'll get a lotta hits.