After doing some internet research, I've come to a theory, or a hypothetical scenerio to maybe explain a little of what is going on here. This may be a long post, so bear with me.
I cam across this website:
http://www.abc.net.au/science/k2/moments/s148725.htm
Which explains a theory of a "Magnetic Sixth Sense" in animals and humans. Basically, it concludes that are tiny "magnets" in the human brain and animal brains that give a sense of direction.
This site :http://lewfh.tripod.com/trees/id1.html
goes further and states that the body is one big electromagnet, with blood assisting in creating this "magnet".
This site:http://www.sciencenews.org/pages/sn_arc99/11_13_99/bob2.htm
explains how electric and magnetic fields (EMF's) can help in curing certian bone disorders.
And this site:
http://www.phy6.org/earthmag/lodeston.htm
explains the lodestone, which is created from magnetite, a "black rock."
Now to tie everything together and explain my theory:
The French scientist came to this island to study the theory of the magnetic sixth sense. The brought polar bears to use because since polar bears are indigenous to the northern hemisphere, they wanted to "mess up" their sense of direction .(just like the students in the article) What better way to do that then by switching poles on them. Once out of their enviroment, the scientist needed to create a man-made magnetic source to see if the polar bears would tune in on that. So, they located a island in the south pacific that had a rather large amount of magnetite. But, the magnetite by itself wouldn't produce a large enough magnetic field to be of use. So, they found a very large "black rock" of magnetite and induced a extemly enormous amount of electric engery to it. (similiar to being struck by lightning, maybe 1.21 Gigawatts, GREAT SCOTT!!!)This may explain the cable. It could of went from a power source (maybe the source had to remain on the boat) to the "Black Rock" somewhere on the island. However, this is where the experiment goes wrong, the magnetic field produced from the "rock" was so large that is started to affect the scientist behaviour. There is a theory that large amounts of magnetic energy can cause a change in human behaviour, including experiencing halucinations...
So basically, they all went mad.
Now, some time later (maybe 16 years?), a flight from Sydney to L.A. comes too darn close to the island and the magnetic field causes the instruments on the plane to malfunction and the pilot reacts in such a way that causes the tails section to rip away form the rest of the plane. (It has happened, I forget which flight) Locke is able to walk too because of the magnetic field, the compass is off because of the magnetic field, and Locke doesn't need the compass anymore because he is in-tune with his "Magnetic Sixth Sense", and he uses the "black rock" as his reference. (Even though he may not know what the source is, his brain is honing in on the direction)
Now for Walt. I theorize that Walt has a condition in his body that creates an abnormal amount of magnetic field. The field is increased even more when he gets angry or exicted, which would cause his heart to beat faster and his blood to flow more. This references the article on the chemical make-up of blood adding to the body being a electro-magnet. When the blood get flowing, Walts magnitism get big enough to attract or throw-off the magnetic sixth sense of lets say birds and polar bears, but not enough to attract metal object. Walt's mom either A)had the same condition in her blood, and her body just couldn't handle it anymore, or B) her blood/body was effected by Walt's magnetism, which maybe became more frequent as his mom and Brian increasely ignored him. The bird scene maybe alluded to this. The comic book and backgammon game could be sure coincindence to lead the viewer down the mystical path of -"This boy has supernatural powers."
So to sum up: The island has a very large "Black Rock" which is really magnetite. French scientist came to the island and transformed the rock in a massive lodestone to perform an experiment in "Magnetic Sixth Sense" using Polar Bears. The magnetic field is so large, that is causes the team to experience erractic behaviour and halluncinations. They are still there: Danielle and the "Others". Who knows how crazy they are by now.
Magnetism causes the plane to crash, Locke to walk, and people having hallucinations (The Beast). Magnetic fields also have a strong attraction/replusion the gravitational force (which affects the tides), so could explain the strange behavior of the tides. Also, maybe the swimmer who drowned had her "magnetic sixth sense" affected and she thought she was swimming parallel to the coast. (For those who have read the diary on the website.)
I can't theorize about the hatch, however. That one still puzzles me...