 This phase II trial studies how well capecitabine and celecoxib with or without radiation therapy works in treating patients with colorectal cancer that is newly diagnosed or has been previously treated with fluorouracil, and has spread to other parts of the body metastatic. Drugs used in chemotherapy, such as capecitabine, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Celecoxib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving capecitabine and celecoxib together with radiation therapy may kill more tumor cells. 