I know this is kindof old, and everyone seems to have agreed on this topic, but after watching Episode I recently, I'm going to have to disagree. When the queen's ship was escaping, several of the shots from the Trade Federation's blockade dissipated above the ship, suggesting it impacted the shields about one or two meters above the hull.
Later, when Anikin landed inside the droid control ship, he had to restart his fighters systems. When he did, you could see the shields activate, and they were only 3 or four inches from the ship's hull. I looked it up on the star wars website, and it said:
Starship deflector shields are projected just a few molecules underneath hull plating, but different power setting and configurations can extend a shield farther away from the hull. Later generation shield projectors could actually support the weight of a starship with its energy.
And:
Since smaller ships have limited power with which to generate deflector shields, they often only protect set areas, or arcs, of the vessel and rely on maneuverability to avoid fire.
It also said that Luke Skywalker developed a tactic by which two starfighters at very close range could network their shield generators to increase strength. This might help to explain the "shield trio" thing that all of the X-wing books talk about.
I realize that what I found on the website contradicts what I saw on the movies, and both of them are official, but it would probably be best to go with the website, because movies don't really have to make sense, as long as they're exciting to watch.
So, basically, capital ships' shields are projected onto their hulls, but some ships can expand their shields, though I'm sure doing so would weaken them by forcing the same ammount of protective energy to cover a greater surface area.
Anyway, have fun!