Patients in this study will receive an unlabeled antibody form of Y2B8 called rituxan by vein followed by a dose of 111In Zevalin by vein. 111In Zevalin includes the radioactive agent indium, which shows up when patients have x-rays or scans. The scans can show where and how fast the drug travels in the body and how long the drug stays in the body. Doctors need to be able to see how much of the drug goes to the tumor and how much goes to normal organs to see if it is safe to give 90Y Zevalin on an outpatient basis. A scan will be taken 48 to 72 hours after 111In Zevalin is given.