Peace, to my knowledge the date for requiring a passport to cross the US border is Jan 1 2008.

"The Departments of Homeland Security and State announced today the Western Hemisphere Travel Initiative to secure and expedite travel. The Western Hemisphere Travel Initiative will require all U.S. citizens, Canadians, citizens of the British Overseas Territory of Bermuda, and citizens of Mexico to have a passport or other accepted secure document to enter or re-enter United States by January 1, 2008."

From: http://www.dhs.gov/dhspublic/display?content=4433