No, I do not believe in ghosts - I believe in science. I do respect people who do believe in them, and I do not claim to have the final answer. I do, however, personally lean up against following scientific discoveries whenever the question of ghosts is brought up:
There is a centre in the human brain devoted to handling with whatever "supernatural" ideas this brain may think up, if it's God, ghosts or something entirely different. Having an epileptic seizure located in this part of the brain can make a Christian person believe they've heard the voice of God or something similar.
I do not believe that anyone claiming to have seen ghosts (or -having- seen ghosts depending on how you look it at it) suffers from epilepsy, but I do think that this centre can receive excessive stimuli and so conjure things before our eyes. This would be why people are more likely to see ghosts in the night, while being alone, preferably after watching a horror movie - all these factors of unease stimulate the "supernatural" part of the brain and people starts seeing things. Do note, however, that I am no brain-scientist-whatever, and I may be speaking bollocks here.
Another point of mine is that the brain is made up purely from fat and enzymes, and our thoughts and emotions are chemical reactions, and as such I find it unlikely that these chemicals should form spirits or ghosts after the brain ceases to function.
My view is as good as anyone's, though, and should anyone come up with a convincing reason for believing in ghosts I would rethink my beliefs again.