As I said in other posts, I think Ben lies about everything when he seems to reveal something to any of the Losties. If there is another land mass nearby, I don't think it has a thing to do with either group except that it may be free of all the wierdness of the island they're on.

After Sawyer's visit to the room where they supposedly installed the pacemaker, we have no way of knowing what they really did to him. They might have just given him a drug to make him accept suggestion easily and he (and we) may have seen the second island only because Ben told him it was there. Remember, there have been a number of times when what we saw on the screen wasn't what really happened. Sometimes they use it for teasers for advertising upcoming shows, sometimes they use the technique as misleading info.

__________________
Things fall apart, the center cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;

--Lines 2-6, "The Second Coming" by Wm. Butler Yeats