In this research study patients will receive dosages of chemotherapy that are lower than the usual dosages. The study will determine whether a shorter duration of immunosuppression will permit the donor cells to be effective against the cancer without causing more severe GVHD (Graft Versus Host Disease). Also to be determined is whether the patient's cancer can be prevented from relapsing after blood stem cell transplant by using prophylactic treatment, giving a donor leukocyte infusion BEFORE a relapse happens.