Computer chiefs at some of the nation's biggest companies have nice things to say about IBM, or nothing to say at all, according to a survey in the forthcoming issue of InformationWeek. Ninety-three percent of the corporate information managers who responded to the InformationWeek survey agreed that International Business Machines Corp. is a positive influence on the marketplace, while none disagreed and 7 percent said they were undecided. But of the 50 executives invited to participate in the survey, 19 declined to participate in spite of promises of anonymity. Their names were chosen from the top echelon of the Fortune 500 and InformationWeek's own list of the 100 biggest computer users. On other questions, 26 percent said IBM exerts unfair influence on the competition while 58 percent disagreed and 16 percent said they were undecided. Sixteen percent said IBM was too big, while 58 percent disagreed and 26 percent were undecided. Sixty-four percent said IBM was fairly treated by the media, while 13 percent disagreed and 23 percent were undecided. The report is part of the magazine's special IBM issue, due out Monday. Because of the small and select size of the sample, the results are not necessarily applicable to computer users in general.