Tarik and the Island of Adventure by Lee Kessell
Tarik knows that his computer is not an ordinary one. When it boots up it makes his favourite smells - hot milky chocolate drink for instance. He feels it is a friendly computer. One day it offers him a strange new game designed just for him. The computer warns him that it is dangerous but he takes no notice. Then he does notice something. The boy in the game is...himself. Far from being friendly, Tarik's computer is sucking him into a threatening world. It is determined to win the game against him. He must discover how to stop it winning...or he, his sister Penelope and his best friend Eddy could lose their lives.