Warren Buffet gets into show-business --Besides guesting in ''All My Children,'' he plays the ukulele on son Peter's album

Has the show-business bug bitten Warren Buffett? In addition to guesting on ABC’s All My Children on Nov. 18, the new chairman of Wall Street’s Salomon Brothers plays ukulele on son Peter’s next LP. Peter, who recently hit the top 10 on Billboard’s New Age Albums, says, ”My father’s not afraid to stick his neck out,” and hopes he and Dad will be joined by distant cousin Jimmy Buffett on the record.