Producers Damon Lindelof and Carlton Cuse revealed in this recap that the reason some survivors were transported to 1977 and others remained in the present was because they were unable to exactly replicate the conditions of Flight 815 aboard Flight 316. Minor differences caused the survivors to successfully crash on the Island, but not exactly as they had planned.
Benjamin Linus's intentions when he met Locke off-Island are more explicitly detailed. Ben did not want to lose his role as the "leader" of the Others, and by manipulating and killing Locke, he could possibly regain his position. He first listened to Locke in order to gain information about Eloise Hawking and the Oceanic Six in order to know how to return after killing him.