Play the King's Indian by Joe Gallagher is absolutely awesome. Angus Dunnington has a 2nd edition of a book on the KIA, and Pirc Alert!, by Alburt is probably the best book on Understanding and playing the Pirc, although the chapter on the classical variation gives bad lines. They were fine at the time, now they're not. So maybe get a newer book to update the theory, but Pirc Alert! has a substantial amount of material on understanding the ideas and structures of the opening. Also, Mikhail Golubev has a recent book out called "Understanding the King's Indian", also very good. Gallagher and Golubev are not only experts on the KID, but they played it themselves alot, so it's good to know they stand behind what they write.