PATIENT CHARACTERISTICS: Age: 1 to 21 Performance Status: ECOG 0-2 Life Expectancy: At least 8 weeks Hematopoietic: Platelet count greater than 40,000/mm3 Hepatic: Bilirubin less than 2.0 mg/dL ALT less than 5 times upper limit of normal Renal: Creatinine less than 1.5 mg/dL Other: Not pregnant or nursing Negative pregnancy test Effective contraceptive method used by fertile patients No uncontrolled illness or infection (except for HIV positive patients) No obstructive hydrocephalus or compartmentalization of the CSF flow