This research study will test the safety of the investigational drug, ZD6474, in combination with 2 other drugs that are standard in the treatment of colon and rectal cancer (cetuximab and irinotecan). ZD6474 blocks the action of two substances in the body: vascular endothelial growth factor receptor (VEGFR) and epidermal growth factor receptor (EGFR). VEGFR stimulates the formation of new blood vessels. When cancer cells produce VEGFR, new blood vessels are made that provide blood to the cancer cells. The blood carries nutrients and oxygen, allowing the cancer cells to live and grow. EGFR controls how quickly cells grow and multiply. Both of these substances are found on normal cells, but they are found in much higher levels on cancer cells.