Is there a way to create a puzzle where the computer will make the first move? I want the human to play White and solve the puzzle but I want the computer to first make a move for Black. Tactics Trainer puzzles sometimes start that way but I don't see a way in the Analysis Editor to set up a puzzle like that. A reason for doing it might be if Black's move allowed an en passant capture. If I set up the puzzle after Black's move and with White to move, then the reader wouldn't know that Black's last move allowed en passant. But that's not the only reason I might want to show Black's last move so I'm looking for a general answer not something specific to en passant.

Good suggestion.

If you're able, you might try to cleverly compose the puzzle so that black's only possible last move was the pawn push that enabled En Passant it will be that much better for it:

http://www.chess.com/forum/view/more-puzzles/mate-in-one2