in "en passant", you can only take the first time that they put you in
the position to do so; i just moved e4, you are f4; if you don't take it
on the next move, than you lose the " en passant!!" you have to take
it on the first move after they move thier pawn out. if you snooze, you
lose, so take it the first time!! that is if it has an advantage!!
i have actually used the en passant to gain position in a game, and it
worked...although, i had to remind the person of it with a subtle: " oh
damn, i forgot about " en passant!!"
well, enjoy...and have fun; that is what it is about after all!!