Hi-tech publisher Ziff-Davis Inc., New York, generated $399.9 million in its initial public offering April 29, making it the second-largest IPO of the year. But the publisher of PC Magazine, PC Week, Computer Shopper and the ZDNet.com Web site did not start off as well as some analysts predicted because the attraction of its Internet presence was offset by the announcement that it would assume $2.5 billion in debt from parent Softbank Corp., Tokyo. Ziff-Davis chairman and CEO Eric Hippeau said the company will use part of the money from the IPO to repurchase ZDNet and other properties from Softbank. The company also will unveil ZDTV, a 24-hour computer-information cable channel, May 11. Ziff-Davis (ZD), which trades on the New York Stock Exchange, opened at an asking price of $15.50 and closed April 30 at $18.