The purposes of this study are to examine the effects of a new combination of drugs, celecoxib (Celebrex®) and irinotecan (CPT-11), with standard radiation therapy on people before they undergo surgery; to determine what effects this combination has on pancreatic cancer; and to determine the highest dose of celecoxib and irinotecan that can be given safely without causing severe side effects. While not an endpoint, it is hoped that this combination will also shrink tumors enough for excision.