Temsirolimus in Combination With Gemcitabine in Previously Untreated Metastatic Pancreatic Cancer

* Because this is a study to determine the highest doses of temsirolimus and gemcitabine that can be given safely together, groups of 3 subjects will be treated at gradually increasing doses of the drugs. Each group of 3 subjects must complete 4 weeks of treatment (1 cycle) before the following group of 3 subjects can start treatment at the higher dose of drug. * Temsirolimus will be given intravenously every week of the 28 day treatment cycle (days 1, 8, 15, 22). Gemcitabine will be given intravenously every other week of the treatment cycle (days 1. 15). * During the study, participants will have weekly clinic visits where the following tests and procedures may be performed: Physical exam; vital signs; urine test; blood tests. * A CT scan will be performed after every 2 cycles (8 weeks) to assess teh response of the tumor to the study treatment.