 RATIONALE: Monoclonal antibodies such as rituximab and yttrium Y 90 ibritumomab tiuxetan can locate cancer cells and either kill them or deliver radioactive cancer-killing substances to them without harming normal cells. Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Combining rituximab and combination chemotherapy with yttrium Y 90 ibritumomab tiuxetan may kill more cancer cells. 