Posession

I saw "the exorcism of Emily Rose" over the weekend and it brought to mind some things I guess I've never though much about.

Such as:

Is there a distinction between spirits and ghost?

Are demons real? Or are they called something else if your not a christian or a catholic?

can a ghost harm you? What about a Spirit?

That's all I can think of for now... I'll let you brew over these for a while and then post my thoughts.