With today's edition, the Business section inaugurates new columns on the financial markets and a new page devoted to markets coverage. Tom Petruno has joined The Times to write a column on stock, credit, currency and commodities markets that will appear Mondays, Wednesday and Friday. On Wednesdays and Fridays, Petruno's Market Beat column will appear on page 3. On Monday, it will anchor a new Market Watch page. Market Watch, page D5, also will include a column on Wall Street's latest deals by syndicated writer Allan Sloan and tables on the performance of stocks, mutual funds and foreign markets.