`ANDREW WYETH: THE HELGA PICTURES' EXHIBITION opens Oct. 28 at the Museum of Fine Arts in Boston. Tickets for a reserved date and time to see the 140 drawings and watercolors of Andrew Wyeth's next door neighbor go on sale Sept. 8 at Ticketron outlets in the United States and Canada. The exhibition remains through Jan. 3, 1988. THE MARGARET MEAD FILM FESTIVAL comes to New York's American Museum of Natural History Sept. 14-17 with over 50 documentary films from 20 nations. Specially featured movies, which explore multicultural and current-event topics, include ``Born Again,'' ``Threat,'' ``Daughters of the Midnight Son,'' and ``What is a Jew to You?'' A SEQUEL TO THE MOVIE `CROCODILE' DUNDEE' is scheduled for release next summer by Paramount Pictures Corp. Paul Hogan will again play Michael J. (Crocodile) Dundee, the charismatic outback Australian, and Linda Kozlowski returns as the American journalist with whom Dundee fell in love. ``Crocodile' Dundee II'' will be produced and directed by John Cornell. A SPECIAL TWO-HOUR EPISODE OF `MATLOCK', an NBC series, will be telecast Sept. 22. In ``The Billionaire,'' a season prem`iere, Matlock travels to London and conducts a mock re-trial to establish a new defense for Eric Gordon, who has been convicted of killing his rich father.