Combination Chemotherapy Followed by Radiation Therapy in Treating Patients With Medulloblastoma, Supratentorial Primitive Neuroectodermal Tumor, or Ependymoma

RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining more than one drug or combining chemotherapy with radiation therapy may kill more tumor cells. PURPOSE: Phase II trial to study the effectiveness of combination chemotherapy followed by radiation therapy in treating patients who have surgically resected, newly diagnosed medulloblastoma or supratentorial primitive neuroectodermal tumor, or incompletely resected ependymoma.