To decrease the risk that leukemia will develop in the brain, you will be given treatment to the brain by an injection into your spinal fluid with methotrexate around Day 2. Ara-C will be given by an injection into your spinal fluid on about Day 7 of the course. The total number of these treatments may be up to 8, which means that you will have 2 with each course until the total number of these treatments is reached. During Courses when you receive nelarabine, injections into your spinal fluid will be given later (around Days 15 and 22 of each course). An Ommaya reservoir may also be surgically placed as a route to treat leukemia in the brain or to decrease the risk of leukemia in the brain. It would be placed in participants who have difficulty with the spinal treatments. An Ommaya reservoir is a tube inserted under the skin of the scalp that enters into the spinal fluid cavity of the brain.