DVD -- who played Bert in the 1964 classic -- was out in Malibu this week ... and told TMZ he was super-excited about Tom Hanks playing Walt Disney in an upcoming movie about the making of "Mary Poppins."

But Dick explained ... there was some MAJOR DRAMA behind the scenes, telling us author P.L. Travers -- who created the Mary Poppins children's books -- battled Disney for 20 years before begrudgingly allowing him to make the film.

"She didn't want to do it," Van Dyke says ... "She just hated the idea ... she hated Julie [Andrews] and she hated me."