Not entirely true. While Mexico has very tight gun control laws civilians can own firearms. As a foreign national however you would not be alowed to bring any ammunition or firearms with you across the border without special clearance. Such permits are usually granted for hunting, however CCW is possible in Mexico if you can demostrate the need for a permit (hard to do, think California). Pistol calibers are limited to .380 and smaller for automatics, and .38 or smaller for revolvers. Any rifles in military calibers are off limits.Mexico has a total wepons ban for civilians. Getting caught with a stray round of ammo in your trunk can get you thrown in the hole. Then it's time to start bribing your way out of jail.
While that sounds like a good book I wouldnt make it my sole source of information. If you have any doubts as to the legalities regarding CCW in a state call the State Police of that state before you travel. They can tell you if your permit is valid in thier state, as well as answer any other questions you may have. The problem with books is that they may not reflect the current laws."Traveler's Guide to the Firearms Laws of the Fifty States"