TBILISI, Georgia - A device, possibly a hand grenade, was thrown toward the stage on which President Bush addressed 300,000 cheering Georgians on Tuesday, but it was not discovered until after the president's appearance, NBC News has learned. It was the only incident to mar what had been a triumphal appearance by the president in the former Soviet republic, where he said Georgia to the world that determined people can rise up and claim their freedom from oppressive rulers.