A positive outlook from No. 2 personal computer maker DellComputer triggered a surge of buying Thursday, the latest swingfor the troubled U.S. stock market. The Nasdaq Composite rose146.20 to 1785.00, while the Dow Industrials rose 402.63 -- 4.23%-- to 9918.05. Volumes were extremely heavy. Dealers welcomedthe heavy buying, but warned that the market remains vulnerableto new disappointments. Despite the day's gains, the Nasdaq isstill down 37 percent from its best level in January. Unlike Ciscoand Nortel Networks, Dell Computer did not issue a secondwarning for the quarter, a welcomed relief for the batteredtechnology sector.