Methotrexate will be given in combination with Ara-C during Courses 2, 4, 6, and 8. You will receive methotrexate by vein over 24 hours on Day 1. You will receive Ara-C by vein on Days 2-3, over 2-3 hours every 12 hours for a total of 4 doses. Doses of Ara-C will be adjusted according to the level of methotrexate you receive. Blood (about 1 teaspoon) will be drawn to measure the study drug level. Leucovorin, used to help decrease the side effects of methotrexate, will be given by vein (over 15 minutes) or by mouth (every 6 hours) for 2-3 days (or until the blood level of methotrexate is low enough to stop leucovorin). Filgrastim will be given at the same dose and schedule as during Courses 1, 3, 5, and 7. You may receive pegfilgrastim given as one dose under the skin rather than filgrastim.