On Days -6 and -4, you will receive gemcitabine by vein over 40-180 minutes. The dose you receive will be based on when you join the study. The length of time it takes to infuse the gemcitabine will be based on when you join this study and the dose amount you are assigned. Up to 6 dose levels of gemcitabine will be tested. Up to 3 participants will be enrolled at each dose level. The first group of participants will receive the lowest dose level. Each new group will receive a higher dose than the group before it, if no intolerable side effects were seen. This will continue until the highest tolerable dose of gemcitabine is found. After the highest dose is found, additional participants will be enrolled at that dose. The number of patients in the group that receives the highest tolerable dose will depend on how many have been enrolled in the other groups.