Busulfan, Melphalan, and Thiotepa Followed By a Donor Stem Cell Transplant in Treating Patients With High-Risk Ewing's Tumors

DISEASE CHARACTERISTICS: * Diagnosis of high-risk tumors of the Ewing's family as defined by 1 of the following: * Biopsy-proven disease with distant metastases to sites other than the lung * Relapsed disease after completion of prior standard front-line therapy or high-dose chemotherapy * Currently in complete remission (CR) with no evidence of disease (with or without minimal residual disease) or very good partial remission (i.e., CR with an abnormal bone scan) after prior standard or high-dose chemotherapy with local control * HLA-compatible stem cell donor available * Compatible donors include those matched at both HLA-A, -B, -C, -DR and 1 of 2 -DQ alleles by high-resolution molecular typing * Related or unrelated donor PATIENT CHARACTERISTICS: * Karnofsky performance status (PS) 70-100% (≥ 16 years old) OR Lansky PS 70-100% (\< 16 years old) * LVEF \> 50% at rest * SGOT \< 3 times upper limit of normal * Bilirubin \< 2.0 mg/dL (unless liver is involved with disease) * Creatinine normal AND/OR creatinine clearance \> 60 mL/min * Lung diffusion capacity \> 50% of predicted (corrected for hemoglobin) OR asymptomatic with a room air oxygen saturation of ≥ 98% * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * No active uncontrolled viral, bacterial, or fungal infection * No HIV-1 or -2 positivity PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No prior therapy with 100 mg/m² of melphalan * No pri…