The purpose of this study is to determine if Velcade (also known as bortezomib) can help prevent graft versus host disease (GVHD) developing after transplantation. This is done by using a combination of three immune suppressive medications: Velcade, tacrolimus and methotrexate. Stem cell transplantation is one of the options for patients with cancer of the blood or blood forming organs. Recently, allogeneic stem cell transplants have been performed using lower doses of chemotherapy and radiotherapy: non-myeloablative or "mini" transplants. GVHD is a significant problem that may occur even after "mini" transplantations. Information from other research studies, suggests that Velcade may help to reduce the risk of developing GVHD when given early after transplantation.