Stocks toggled in and out of mixed terrain in the early going Thursday. A half-hour after the open, the Dow Jones industrial average and the S&P 500 were down a fraction each. The Nasdaq was up by an equal amount. Volume started mixed, up 37% on the Nasdaq and down 5% on the NYSE, compared to action at the same time Wednesday. The stock market today opened groping for direction. Overseas markets were generally positive.