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 PRIOR CONCURRENT THERAPY: Biologic therapy: * At least 1 week since prior colony-stimulating factors (e.g., filgrastim \[G- CSF\], sargramostim \[GM-CSF\], or epoetin alfa) * At least 4 months since prior myeloablative therapy requiring bone marrow or stem cell transplantation * No concurrent anticancer immunotherapy Chemotherapy: * See Disease Characteristics * At least 3 weeks since prior chemotherapy (4 weeks for nitrosoureas) and recovered * Prior temozolomide allowed provided not administered within past 3 months, no severe toxicities experienced during prior course, and not given in combination with other agents designed to inactivate alanine-glyoxylate aminotransferase * No other concurrent investigational or standard anticancer chemotherapy Endocrine therapy: * Concurrent corticosteroids for control of brain tumor-associated edema allowed provided on stable or decreasing dose for at least 1 week prior to study Radiotherapy: * See Disease Characteristics * At least 4 weeks since prior limited-field radiotherapy * At least 4 months since prior craniospinal irradiation, total body irradiation, or radiotherapy to more than half of the pelvis * Recovered from prior radiotherapy * No concurrent anticancer radiotherapy Surgery: * See Disease Characteristics Other: * At least 4 weeks since other prior investigational therapy and recovered * No other concurrent anticancer investigational agents