My sister likes to channel old dead guys from Atlantis. There's a reason for that: my sister takes after our father, by which I mean she's batshit crazy.
I don't disbelieve in ghosts. But I believe in what I see, and ghosts would be one of the few things I haven't run into yet, except in the sense that every so often MI13 gets sent out to look into some weird haunted thing which inevitably turns out to be, I don't know, aliens or mutants with a grudge or whatever the flavor of the week is.
I don't believe in much of anything, when you get right down to it. I've seen a lot of strange things, half of them being people I work with; I've flown into Fairyland/England's collective subconscious on a helicopter, and there's this dragon from outer space who talks like a Cockney and thinks stealing my cigarettes is a great gag. Not a lot of belief involved there, just experience. Result of working for the Department of Really Weird Shit. So for me, ghosts are in the same category as God and heaven: I'll believe in it when I see it.