I have seen talk about Ben's box comment in a couple threads, but couldn't find one with this specific topic. So I thought I would start one.
My first impression was that Ben was trying to lure Locke in with false info, and stall for time to prevent Locke from blowing up the sub. A magic box that could produce what ever you could imagine. This is just the kind of weird island thing that Locke would be interested in. But Locke doesn't buy it.
He tells him that if he had such a box then Ben could imagine himself up a new submarine.
Now after seeing the episode, it is clear that Ben wanted Locke to blow up the sub. So whats with the box story. Someone (sorry I forget who) mention that they thought the box was the island itself. This makes some sense, because of the appearence of people and items that are related to the losties
desires.
Examples
Yemi's plane crashed on the island --- Eko
Same plane loaded with heroin ---- Charlie
Kate's horse
Jack's dad
a whole library of books (seems like it) for Sawyer to read
dharma van for Hurley
and other things like this keep popping up on the island.
So I think Ben was using a magic box as an analogy for the island itself. But there are still a lot of loose ends to tie up.