By MARTY BAUMANN and TOM WEAVER The real Pamela Duncan may not believe in reincarnation, but the movie Pamela Duncan lives forever as the star of two of the 1950s most vivid, low-budget thrillers. Many recall her as the savvy lady scientist in Roger Corman's Attack of the Crab Monsters. But it is her role as the hypnotically-regressed streetwalker, Diana Love, in Corman's claustrophobic film, The Undead, for which Duncan may be best remembered. "I think that film was underrated," she submits. "The title made you think there were zombies in it. Actually, it was the Bridey Murphy story."