WASHINGTON (Reuters) - The Pentagon has begun drawing up plans to send troops and equipment to the U.S. border with Mexico, where hundreds of thousands of migrants enter the country illegally each year, a defense official said on Friday. Defense Secretary Donald Rumsfeld discussed border issues at the Pentagon with his Mexican counterpart, Defense Minister Gen. Gerardo Clemente Ricardo Vega. Mexico and the United States share a 2,000-mile border. "The U.S. and Mexican governments continue to work together to control the border and collaborate on these important efforts," said U.S. Navy Lt. Cmdr. J.D. Gordon, a Pentagon spokesman. "This cooperation...