It is possible to reduce the amount of radiation delivered to the normal tissues that surround cancer by using an advanced radiation therapy delivery technique called intensity-modulated radiation therapy (IMRT).  The purpose of this study is to determine whether reducing the amount of radiation, given along with chemotherapy, to these normal tissues will reduce the side effects associated with standard radiation and chemotherapy treatment for rectal cancer. The chemotherapy used in this study are commonly given for rectal cancer.  The research part of this study is looking at the use of IMRT with the chemotherapy.