Be careful my brother did with some friends and says he summoned something. He said it was an old women in blue, who seemed to have died in a fire. He tested this by placing five lighters in row on his bed and left the room, when he came back in they were scattered.
Now I do believe in ghosts as I feel them (I'm actually psychic), and have seen them. There's a few that hang around my house that I've seen, one is a woman and one's a man. The last is a dog which I think is the spirit of my dog Sadie. All are friendly, though they like to knock on things. :)