You will take the chemotherapy drug capecitabine by mouth twice a day as a tablet on each of the days that you receive radiation therapy. These pills will not be taken on Saturday and Sunday. You must not be taking the drug cimetidine, and must be off of coumadin for at least 1 week and sorivudine and brivudine for at least 4 weeks before starting capecitabine and during the entire capecitabine therapy. If you are not able to stop taking coumadin, you will need extra blood tests performed throughout the study to check your bleeding and clotting speed.