This has recently changed according to the us dept. of state website
http://travel.state.gov Here are some of the frequently asked questions from that page:
When will the Travel Initiative be implemented?
In the proposed implementation plan, which is subject to a period of initial public comment, the Initiative will be rolled out in phases, providing as much advance notice as possible to the affected public to enable them to meet the terms of the new guidelines. The proposed timeline will be as follows:
December 31, 2006 Requirement applied to all air and sea travel to or from Canada, Mexico, Central and South America, the Caribbean, and Bermuda.
December 31, 2007 Requirement extended to all land border crossings as well as air and sea travel.
I thought there was an additional phase to be implemented on December 31, 2005. Is this a change?
In April 2005, the Departments of State (DOS) and Homeland Security (DHS) announced a proposed plan to be implemented in three phases beginning on December 31, 2005 for the Western Hemisphere Travel Initiative. After further review and considering the delay in publishing the public notice in the Federal Register, DOS and DHS recognized that implementing the December 31, 2005, phase would be problematic for travelers during the upcoming winter tourism season. This change will simplify the implementation and provide a longer lead-time for travelers to come into compliance with the requirements.
Hope this helps!