Was the Septuagint used in the translation of the King James Version (KJV) of the Bible? Is it just for the Old Testament or the New Testament?
For the old testament, the Septuagint was used over the Masoretic test, where the reading found in it supported traditional Christian doctrine, more so than the reading found in the Masoretic text i.e. Psalm 22:16 "they pierced my hands and my feet."
To answer the second part of your question, the Septuagint predates the new testament, so it contains the old testament, and some of the apocryphal books.
Finally, as Susan points out in the comments below, the Hebrew Masoretic text was the primary text used for old testament. The Septuagint was used primarily for the Apocrypha, with the Vulgate was used for apocryphal books not found in the Septuagint (i.e. 2 Esdras), and Erasmus' Textus Receptus was used for the new testament.