Conan O'Brien is expected to draw a massive audience for his final appearance as host of The Tonight Show tonight -- the last night he will be able to fire humorous insults at NBC executives -- at least until next September. News reports on Thursday indicated that his $45-million separation agreement includes a standard nondisparagement clause that takes effect after tonight and effectively acts as a nine-month gag order. The Wall Street Journal , citing unnamed insiders, reported today (Friday) that the agreement contains restrictions barring him from doing interviews during the nine-month period. (Today's New York Times said that the network was concerned that O'Brien might seek to undermine Jay Leno's return to The Tonight Show by appearing as a guest on the David Letterman show on CBS or with Jon Stewart or Stephen Colbert on Comedy Central on March 1, the day Leno resumes hosting the NBC late-night show.) O'Brien is unlikely to challenge the restriction, persons interviewed by the Journal indicated. "He has 45 million reasons to not disparage anyone," Hollywood talent manager Eric Gold told the newspaper. Meanwhile, it appeared that Jay Leno's deal to return to his old time period contained no such nondisparagement clause. On his show Thursday night he announced, "I have chosen to stay on the Titanic."