Temozolomide and O6-benzylguanine in Treating Children With Solid Tumors

DISEASE CHARACTERISTICS: * Histologically confirmed solid tumor refractory to standard therapy and for which no potentially curative therapy exists, including, but not limited to: * Rhabdomyosarcoma and other soft tissue sarcomas * Ewing's family of tumors * Osteosarcoma * Neuroblastoma * Wilms' tumor * Hepatic tumors * Germ cell tumors * Primary brain tumor * Histological confirmation may be waived for brainstem or optic gliomas * Measurable or evaluable disease * Evidence of progressive disease on prior chemotherapy or radiotherapy or persistent disease after prior surgery PATIENT CHARACTERISTICS: Age: * 21 and under Performance status: * ECOG 0-2 Life expectancy: * At least 8 weeks Hematopoietic: * Absolute granulocyte count greater than 1,500/mm\^3 * Hemoglobin greater than 8 g/dL * Platelet count greater than 100,000/mm\^3 Hepatic: * Bilirubin normal * SGPT less than 2 times upper limit of normal * No significant hepatic dysfunction Renal: * Creatinine normal OR * Creatinine clearance at least 60 mL/min Cardiovascular: * No significant cardiac dysfunction Pulmonary: * No significant pulmonary dysfunction Other: * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Able to swallow capsules * No significant unrelated systemic illness that would preclude study (e.g., serious infections or organ dysfunction) * No prior hypersensitivity to dacarbazine, temozolomide, or polyethylene glycol…