HANOI (Reuters) - Thousands of Vietnamese students climbed trees and pushed against barricades to give Microsoft founder Bill Gates a pop star's welcome in Hanoi on Saturday. The world's richest man is on a one-day visit to the impoverished Southeast Asian country, which has the highest rate of fake software sold in the world, according to trade groups. With annual per capita income of $640 (360 pounds), few can afford Microsoft packages and pirated versions sell for a dollar or two. "I hope that one day I can be as successful as him," said Nguyen Trung Dung, 19, one...