1. Kingdom Hearts 2 comes out this winter. They haven't set a firm date yet, but they're saying sometime in November.
2. The story is complicated as hell but I'll try and explain what I can. I'm going to get a few details wrong since it's been about a year since I've won the game, but here goes. The ruler of a nameless world named Ansem discovered creatures called the Heartless. While studying them he became corrupted by them and their dark power turned him into an evil person set on destroying the the universe.
As the Heartless were becoming more powerful and going from world to world through the keyholes destroying them, the power of the Heartless was noticed by the Disney villians lead by Malificent. She along with the others thought she could control their dark power and use it to her advantage. Their plan was to use the Heartless' power to capture all the Princesses of Heart.
So as the worlds were being destroyed eventually Destiny Island's turn came up and then entered Sora, Kairi, and Riku. When their world was destroyed, the three characters got separated from one another. Sora would become the Keyblade Master and went from world to world locking them in order to seal them away from being taken over by the heartless. Kairi turned out to be a Princess of Heart, but seems to immediately have been captured by the villains. Riku got tricked into joining the Disney villains in order to find Sora and Kairi, but was also possessed by Ansem.
As Sora's journey goes on he eventually defeats the Disney villains and rescues all the Princesses of Heart. Once he reaches the end of the world he discovers that Ansem was just using Riku's body when Ansem sets him free in order to use the full power of the Heartless.
At the end of the game the Heartless get sealed back in their realm behind the white door, but in order to shut it Mickey and Riku had to pull it closed. Where the two of them end of is never explained, but will more than likely be explained in KH2. It is assumed that Kairi was sent back to Destiny Island, but that could have just been another one of Sora's dreams.
Anyway hope that helped. Probably didn't but it couldn't hurt to try. Gamefaqs in all likelihood is a good place to start.
