Stocks stepped up Friday, albeit in lower volume, handing the Nasdaq and S&P 500 their sixth straight weekly gains. The Nasdaq rose 0.9%, the S&P 500 0.6% and the Dow Jones industrial average 0.4%. Volume in the stock market today was down from Thursday's levels across the board. For the week, the Nasdaq and S&P 500 advanced 0.5% and 0.3%, respectively. The Dow pulled back 0.1% for the week and closed under the 14,000 level, after advancing for