ANDREW S. CLARKE is a senior financial writer at The Vanguard Group. Before joining Vanguard, he worked for Morningstar, the investment research firm. Mr. Clarke is a Chartered Financial Analyst.JOHN J. BRENNAN is the Chairman and Chief Executive Officer of The Vanguard Group and author of the bestseller, Straight Talk on Investing, also published by Wiley.THE VANGUARD GROUP is the world's second-largest mutual fund company, with 15 million shareholder accounts and $600 billion in assets under management. Vanguard pioneered low-cost index mutual funds, and has distinguished itself as a champion of superior client service and low investor costs.