The United States wasn't really prepared for an attack on Pearl Harbor because the United States was focusing on Europe at the time, and trying to keep Great Britain from being conquered by Germany and Italy. It had been doing so for two years, with no mention of trouble from Japan.
The United States never expected Japan, which had its' focus on China, India, and Australia, to suddenly do an about-face and attack Hawaii in 1941. Keep in mind - at this point in history, Hawaii wasn't a state. It was just a foreign territory of the United States, mainly used as a vacation residence for rich people, as well as a military base.
Also, it wasn't just Hawaii. Wake Island was attacked a couple hours after Hawaii, but was a little more prepared after having received some news of the Hawaiian attack. Still, Wake Island went under after several days as well, and was held by the Japanese until 1945.
Another attack was on Alaska, when the islands of Attu and Kiska were attacked and overcome by the Japanese in 1943, and held for several months before the Japanese realized they couldn't advance any further into Alaska for one reason: Alaska had been built up by the military in preparation for an invasion from the Soviet Union, which at the time, was a member of the Axis, before being betrayed by the Germans.
Don't pay much attention to the movie "Pearl Harbor". Instead, watch the older, more accurate movie, "Tora, Tora, Tora". It's not as exciting, and it's in black and white, but it's much more accurate historically. The final battle is better too.
The Japanese made two major mistakes with the attack on Pearl Harbor. The first was that they overextended their reach, biting off more than they could chew. If they had remained in the Far East, fighting in China, India, Indochina, Australia, the Philippines, and New Zealand, they could have pulled together more resources to fight the United States.
The second mistake was, once they decided to attack Pearl Harbor, they didn't follow up the attack. They bombed Pearl Harbor to bits, leaving plenty of room for an invading force to take over the Hawaiian Islands with ease. Instead, they focused their attack on Wake Island, and lost a great many planes, ships, and men. If they had ignored Wake Island, and instead focused on Pearl Harbor, the outcome in the Pacific Theater might have been very different.
I hope this has answered your question. If you have any more, please feel free to ask.
Sorry, I can't link to a movie. Go rent "Tora, Tora, Tora" from Family Video, Netflix, or Blockbuster.