A Guide to Navigate the TV Maze Gives Pause
Gemstar-TV Guide International, which produces interactive TV guide and channel navigator, has amassed so much power that Justice Dept has asked to review its business documents because of accusations by competitors that it has built monopoly; Gemstar, headed by Henry C Yuen and part-owned by Rupert Murdoch's News Corp, says company simply gives viewers ability to make informed choices in rapidly changing media environment, especially for digital- or satellite-television subscribers trying to make sense of dizzying array of channels; says it operates within antitrust laws; in fact, its programming guide may influence what viewers watch because some of what is seen on screen are advertisements; photos (M)