Combination Chemotherapy Followed by Peripheral Stem Cell Transplantation or Bone Marrow Transplantation in Treating Patients With Brain Cancer

DISEASE CHARACTERISTICS: * Diagnosis of one of the following malignant brain tumors: * Anaplastic astrocytoma * Glioblastoma multiforme * Anaplastic oligodendroglioma * Medulloblastoma * High-grade ependymoma * Germ cell tumors * Pineoblastoma * Other primitive neuroectodermal tumors * Recurrent disease or resistant to conventional therapy (e.g., surgery, radiotherapy, or standard chemotherapy) * No prior myeloablative doses of thiotepa OR * Newly diagnosed malignant glioma with minimal residual disease after prior radiotherapy * Minimal residual disease is defined as tumor with maximum diameter of less than 1.5 cm by MRI and no corticosteroid dependency PATIENT CHARACTERISTICS: Age: * Over 1 to under 50 Performance status: * Karnofsky 70-100% OR * Lansky 70-100% Life expectancy: * More than 12 weeks Hematopoietic: * Absolute neutrophil count at least 1,500/mm3 * Platelet count at least 100,000/mm3 * Hemoglobin at least 10 g/dL (transfusion allowed) Hepatic: * Bilirubin less than 1.5 times upper limit of normal (ULN) * SGOT/SGPT less than 2.5 times ULN * Alkaline phosphatase less than 2.5 times ULN Renal: * Creatinine less than 1.5 times ULN * Creatinine clearance at least 70 mL/min * BUN less than 1.5 times ULN Cardiovascular: * Ejection fraction greater than 50% OR * Shortening fraction greater than 27% * No evidence of myocardial ischemia on EKG if over 40 years of age Other: * HIV negative * No AIDS-related illness * No frequent vomiting or medical condition that would preclude oral medication (e.g., partial bowel obstruction) * No other malignancy within the past 2 years except surgically cured carcinoma in situ of the cervix or basal cell or squamous cell skin cancer * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * At least 2 weeks since prior biologic therapy or immunotherapy Chemotherapy: * See Disease Characteristics * At least 4 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin) and recovered Endocrine therapy: * See Disease Characteristics Radiotherapy: * See Disease Characteristics * At least 6 weeks since prior radiotherapy and recovered * At least 6 weeks since prior brachytherapy or radiosurgery Surgery: * See Disease Characteristics * Recovered from prior major surgery