During treatment you will be given a combination of three drugs in a 21 day (3 weeks) cycle. All drugs will be given through a needle in a vein over 4-6 hours. You will receive pentostatin first, then rituximab, and lastly cyclophosphamide. For each treatment cycle cyclophosphamide, rituximab, and pentostatin will be given on Day 1, followed by 20 days of rest.