I haven't used rpg maker 2k3 but Im pretty sure it may have an option in the event editor called conditional branch, all you have to do is create a person and in the persons event editor use the option called conditional branch and make it so you need the item, then make it so if you talk to the person with the item then they will give you your reward and you lose the quest item and if you don't have the quest item with you then they might say, please get me the item I need, sorry if this is a bit confusing but I haven't used rpg maker 2k3 for a long time.