Blow up the earth at the top on the right hand side underneath and then walk the leader under where itwas. this isn't a hidden level just aa strange quote and aphoto hidden there of the people who did the game.
Level 42 "BASKETCASE"
There's an image hidden in the brickwork under the rocket. drop bombs in the gap below the leader. (I think the picture is of something from a doom level that the programer was making but the page is gone from the Hungry Software site now)