PHASE I: Patients receive temsirolimus intravenously (IV) over 30-60 minutes on days 1, 8, 15, and 22; rituximab IV over 30-60 minutes on days 1, 8, 15, and 22 (of courses 1 and 4 only); and bortezomib IV or subcutaneously (SC) and dexamethasone orally (PO) on days 1, 8, and 15. Courses repeat every 28 days for up to 6 courses in the absence of disease progression or unacceptable toxicity.