Non-Ablative Allo HSCT For Hematologic Malignancies or SAA

DISEASE CHARACTERISTICS: * Histologically proven high-risk hematologic malignancy * Acute non-lymphocytic leukemia (ANLL) after induction failure, or in first complete remission (CR) with high-risk features, including any of the following: * Stem cell or biphenotypic classification (AML-M0) * Erythroleukemia (AML-M6) * Acute megakaryocytic leukemia (AML-M7) * Cytogenetic markers indicative of poor prognosis * Failure to achieve CR after standard induction therapy * Acute lymphocytic leukemia (ALL) or ANLL in relapse or second or subsequent remission * Chronic myelogenous leukemia (CML) in chronic or accelerated phase * Patients with CML in blast crisis are eligible after reinduction chemotherapy places them in chronic phase * High-risk ALL in first CR with high risk defined by presence of t(4;11), t(9;22) translocation, hyperleukocytosis (initial WBC greater than 30,000/mm\^3), or failure to achieve CR by day 28 after standard induction * No T-cell ALL or t(8;14) positive B-cell ALL in first remission with hyperleukocytosis * Myelodysplastic syndrome by peripheral blood smear and bone marrow examination * Refractory to medical management OR * Cytogenetic abnormalities predictive of transformation into acute leukemia including 5q-, 7q-, monosomy 7, and trisomy 8 OR * Evidence of evolution to AML (e.g., refractory anemia with excess blasts (RAEB) or RAEB in transformation) * Multiple myeloma, non-Hodgkin's lymphoma (NHL), ANLL, or ALL with recurrent disease after autologous stem cell transplantation (SCT) * At least 3 months since prior autologous SCT * Hodgkin's lymphoma, NHL, or multiple myeloma beyond first CR or primary induction failures whose disease has demonstrated sensitivity to pre-transplantation cytoreduction (defined as greater than 50% reduction in tumor burden) * Mantle zone NHL allowed after induction therapy * Myeloproliferative disorder that is non-responsive to medical management and requires allografting, unless evidence of grade 3 or worse myelofibrosis on marrow biopsy OR * Histologically proven acquired severe aplastic anemia (SAA) that is recurrent or unresponsive after anti-thymocyte globulin and/or cyclosporine * SAA defined by at least 2 of the following conditions: * Granulocyte count less than 500/mm\^3 * Platelet count less than 20,000/mm\^3 * Absolute reticulocyte count less than 20,000/mm\^3 after correction for hematocrit * Ineligible for full ablative conditioning due to any of the following conditions: * Prior extensive therapy (more than 2 salvage chemotherapy regimens and/or autologous transplantation) * Over age 55 OR * Under age 55 with comorbid disease (e.g., suboptimal cardiac, pulmonary, or renal function and/or prior life-threatening infection) * HLA-A, B, and DR phenotypically identical sibling donor OR * HLA-A, B, and DR identical genetically matched unrelated donor * No ANLL in first CR (less than 5% blasts in marrow) with translocations t(8;21) and inv(16) unless failed first-line induction therapy OR * No ANLL in first CR (less than 5% blasts in marrow) with translocations t(15;17) abnormality unless failed first-line induction therapy OR molecular evidence of persistent disease * No active CNS disease PATIENT CHARACTERISTICS: Age: * 0 to 70 Performance status: * Zubrod 0-1 * Karnofsky 80-100% Life expectancy: * At least 3 months Hematopoietic: * See Disease Characteristics Hepatic: * ALT/AST no greater than 4 times normal * Bilirubin no greater than 2.0 mg/dL Renal: * See Disease Characteristics * Creatinine clearance at least 50 mL/min Cardiovascular: * See Disease Characteristics * Shortening fraction or ejection fraction at least 40% of normal for age by echocardiogram or radionuclide scan * No clinically significant comorbid illnesses (e.g., myocardial infarction or cerebrovascular accident) Pulmonary: * See Disease Characteristics * FVC and FEV\_1 at least 60% of predicted for age * DLCO at least 60% of predicted for adults Other: * No severe neurosensory symptoms (i.e., peripheral neuropathy) * HIV negative * Active infection allowed if controlled by appropriate drug therapy * Not pregnant or nursing * Negative pregnancy test PRIOR CONCURRENT THERAPY: Biologic therapy: * See Disease Characteristics Chemotherapy: * See Disease Characteristics Endocrine therapy: * Not specified Radiotherapy: * Not specified Surgery: * Not specified Other: * Recovered from prior therapy * No concurrent investigational agents unless approved by protocol investigators