The traditional way of doing a donor transplant is to give high doses of chemotherapy and radiation before giving the stem cells. However, high doses of chemotherapy and radiation can have serious side-effects. The doctors think that the transplant will be safer and more likely to be successful with reduced doses of chemotherapy and radiation. The purpose of this study is to find out how good a combination of chemotherapy and radiation at reduced doses followed by a cord blood transplant are at treating cancer.