Patients receive O6-benzylguanine (BG) IV over 1 hour followed by carmustine IV over 1 hour every 6 weeks for 5 courses, assuming recovery of peripheral blood counts. Approximately 72 hours after the end of the first course of chemotherapy, patients receive reinfusion of retrovirally-transduced hematopoietic stem cells over 5-10 minutes. Four weeks after the completion of BG and carmustine, patients receive BG IV over 1 hour followed by temozolomide IV over 1 hour every 4 weeks for up to 5 courses, in the absence of hematologic toxicity. Patients with responding disease may continue to receive BG and temzolomide in the absence of disease progression or unacceptable toxicity provided other phase II studies indicate the safety of more than 5 courses.