Stocks posted moderate gains Wednesday, boosted by a heartening sign that the job market is improving. The Nasdaq climbed 0.5%, the S&P 500 0.4% and the Dow Jones industrial average, weighed by Hewlett-Packard's (HPQ) 13% plunge, edged up a scant 0.1%. Volume increased on both major exchanges, according to preliminary data. Stocks got a boost from a report by ADP Employer Services, which said the private sector added 162,000 jobs in September.