The S&P 500, widely considered the broadest snapshot of corporate America, slipped 52.54 points, or 6.12 percent, to 806.58; and the Dow gave up 427.47 points, or 5.07 percent, to 7,997.28. Both closed at their lowest levels since March 2003, and are rapidly approaching the lows of the 2000 to 2002 bear market