This phase I trial is studying the side effects and best dose of tipifarnib when given together with temozolomide and radiation therapy in treating patients with newly diagnosed glioblastoma multiforme or gliosarcoma. Tipifarnib may stop the growth of tumor cells by blocking the enzymes necessary for tumor cell growth. Drugs used in chemotherapy, such as temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining tipifarnib, temozolomide, and radiation therapy may kill more tumor cells.