Stage II-III biopsy-proven non-recurrent primary adenocarcinoma of the rectum. Distal border of tumor at or below peritoneal reflection. Patient must have wild-type k-ras (testing may be performed either by a CLIA-certified local lab or by the study's central lab). Measurable and/or non-measurable disease. No prior chemo, RT, or targeted tx for this tumor. No investigational agents within 28 days prior to reg. No prior severe reaction to monoclonal antibody. Must have recovered from any recent major surgeries. Must be willing to submit additional specimens. Zubrod 0-2. No peripheral neuropathy >/= Grade 2. No uncontrolled coagulopathy. No high-grade obstruction. No history of allergy to platinum compounds or to antiemetics. No prior unanticipated severe reaction to fluoropyrimidine tx, known sensitivity to 5-FU, or known DPD deficiency. No inflammatory bowel disease, malabsorption syndrome or inability to swallow that would impair the ingestion or absorption of capecitabine. No uncontrolled intercurrent illness. No ongoing or active infection, symptomatic CHF, or unstable angina pectoris. No cardiac arrhythmia or MI within the last 12 months. Must not be receiving anti-retroviral tx for HIV. Within 28 days prior to reg: assessment of measurable disease; leukocytes >/= 3,000/mcl; granulocytes >/= 1,500/mcl; platelets >/= 100,000/mcl; bilirubin </= 1.5 x IULN; alkaline phosphatase </= 2.5 x IULN; SGOT or SGPT </= 2.5 x IULN; calculated creatinine clearance > 50 mL/min. Within 42 days prior to reg: assessment of non-measurable disease.