SACK RUMOR SACKED
We—and a lot of other people—had been hearing the rumor that the Roseanne and Tom .Arnold marriage was on the rocks because she caught him in bed with another woman. The other night Roseanne addressed those whispers from the stage at the Beverly Hills nightclub Tatou. Seated with Ed Begley Jr. and other friends—Tom was in Washington filming a movie—Roseanne was persuaded to come onstage and sing back-up vocals on "Hot Fun in the Summertime" with the rock band Black and White. In the middle of the song, Roseanne stopped the music and proclaimed, "I just want everybody to know that I didn't catch my husband in bed with anybody. We're still married. So f—off."

THE WRITE STUFF
More trouble looms for Michael Jackson—this time in manuscript form. According to a source close to the deal, Simon & Schuster has entered into a $350,000 agreement with author Christopher Andersen to publish an unauthorized biography of Jackson on the condition that the book will "back up the child molestation allegations" levied against the singer last August in Los Angeles. The source adds that Andersen, whose best-known book is 1991's Madonna, Unauthorized, intends to produce "a child star who is prepared to spill the beans" on Jackson but that the author has yet to identify the child for the publisher. Calling the deal "low-risk" for S&S, the source says that if Andersen delivers as promised, "this will be one big-selling book. II he doesn't, there is no book." And no $350,000 for Andersen.

NO HOLDS BARRED
Being in jail apparently hasn't hurt Amy Fisher's love life. It seems the Long Island Lolita has a new beau, a sergeant at the Albion Correctional Facility, the upstate New York prison where she has been serving part of her 5-to-15-year sentence for shooting Mary Jo Buttafuoco in May 1992. According to a source close to Fisher, "She's madly in love with him, and he's supposedly in love with her." As for where the two go to be alone, our source says, "He can take her to the frisk room or the visiting room, when everybody's gone. It's easy." One of Fisher's lawyers, Matthew Roscnblum, says he knows nothing about any romance.

ACING THE ART WORLD?
When he's not appearing on TV as a tennis announcer, John McEnroe can be found toiling away in the art gallery he recently opened in Manhattan's Soho section. Its name? The John McEnroe Gallery, natch. McEnroe, an eclectic art collector for the past 15 years, recently spent seven months learning the business at a local gallery. According to Robin Zendell, who runs McEnroe's shop, now open by appointment only, the gallery will open to the public in early '94. What will be on view then? Says Zendell: "A combination of works by unrecognized artists and well-known contemporary artists."