I'm afraid I don't believe at all, I think it's a rubbish program and does nothing for anyone who genuinely believes they have 'psychic' abilities, and as for Derek Acorah.... he's a muppet....
One of my favourite sites is this one:
Bad Psychics
they have some very funny clips from Most Haunted of them cheating their pants off.... oh, and you must check out the 'Mary loves Dick' clip they have, the bit that was edited out of the program.... I'll say no more...
Mary loves Dick