The study involves the use of a targeted form of radiation, in addition to standard high dose chemotherapy and stem cell transplant for multiple myeloma. The use of targeted radiation is designed to kill more multiple myeloma cells while avoiding the side effects of standard radiation. This type of targeted radiation (also known as radioimmunotherapy) has been approved by the Food and Drug Administration (FDA) for the treatment of a related disease, lymphoma under the trade name, Zevalin©. Zevalin© has been added to high dose chemotherapy and stem cell transplants for patients with lymphoma and is now being studied in this clinical trial for patients with multiple myeloma. This trial is only available at Tufts Medical Center.