If the admin/mod that programmed the chess game for the site put the option for .pgn in the games? Idk how difficult it will be, but all it would have to do is to mark what the last move is by ways such as [piece pawn isn't needed unless capture][designate if multiple of the same piece can move to that square][x if capture][file][rank]. A wiki can be found here http://en.wikipedia.org/wiki/Portable_Game_Notation