Okay, there is some confusion here, and in part I blame those who try and mess with time, but that's beside the point.
There are two judgments.
One, the particular judgment, happens for each person when he or she dies. The deceased is assigned a foretaste of eternal blessedness or eternal punishment in accordance with his or her deeds. This is not, however, the final or last judgment, which will occur when the Lord Jesus Christ returns to judge the living and the dead, and this world will pass away.
Since the Last Judgment has not yet occurred--if it had, we would not still be sitting in our cubicles typing--the souls of the departed, and our souls as well, are in a state of flux. We who are yet in the body are able to repent, and we are able to pray for those souls who have departed. We pray for them that have died that God may grant them rest with the saints and forgiveness of sins. There are those of the departed, however, who God has shown to be saints, who have grace to pray for us. Our prayer for the dead in some way communicates with them, and by God's grace sometimes they communicate with us. The same goes with our prayers to the saints. The veil between this life and the next is a thin one indeed, and it is only because of our sins that we cannot see how, in truth, God and his saints act in the world.
We know we are guided aright in our prayers for the departed, and our prayers to the saints, because we are instructed by the Church which Christ established and his Apostles spread throughout the world, leaving bishops as their successors. There are those, however, who do not follow the Orthodox way and can be lead into serious error and demonic delusion. We deal with what we know, but they deal with what they do not know, and so are prone to make mistakes.
With regard to the king and the Prophet Samuel, one must look at the context. It would help if this passage were quoted.