 The purpose of this study is to find out whether the monoclonal antibody 8H9 is useful in finding tumors in your body. Antibodies are protein found naturally in blood. They can fasten themselves to bacteria and viruses. They can stimulate white cells and blood proteins to kill tumors. The antibody 8H9 was made from mouse white cells. The white cells that secrete this antibody have been made to live for ever. They manufacture large amounts of 8H9 for patient use. Although other monoclonal antibodies have been safely tested in people, the antibody 8H9 has never been given to a human patient. 