COURSE Vb (autologous PBSCT for patients without HLA-matched sibling donor): Beginning 3-10 days after completion of course IV, patients without an HLA-matched sibling donor receive etoposide IV continuously and cytarabine IV over 2 hours on days 1-4. Patients also receive filgrastim SC beginning on day 14 and continuing until PBSC collection is complete. Patients receive imatinib mesylate PO twice daily beginning after completion of PBSC collection and continuing until 3 days before PBSCT. Patients then undergo TBI 2-3 times daily on days -8 to -5. Patients receive etoposide IV over 4 hours on day -4 and cyclophosphamide IV over 2 hours on day -2. Patients undergo PBSCT on day 0. Patients receive filgrastim SC beginning on day 0 and continuing until blood counts recover.