The objectives of this study are to determine the maximum tolerated dose of 5-Fluoro-2'-Deoxycytidine (FdCyd) administered by IV infusion over 3 hours with concurrent infusion of 35mg/m2 of tetrahydrourdine (THU), and to evaluate the pharmacokinetics of these 2 agents given together. When feasible, will measure the relative levels of the mRNA's for thymidylate synthase, deoxcytidine kinase, dCMP deaminase and other relevant enzymes, and the methylation satus of p26 and other genes revelant to neoplasia. Infusions will be given on days 1-5 every 21 days.