 Purpose: This study will evaluate the safety and efficacy of clofarabine for aggressive NHL. Toxicities resulting from the combination of clofarabine and the supportive care drug GM-CSF will also be analyzed in patients. GM-CSF is a blood-forming agent that stimulates the production of white blood cells. In addition, several tests, including blood and tumor tissue analysis, will assess immune response and biological changes to the tumor as a result of study drugs. 