The newest release of ChessNET supports Castling, En Passant, and the 50 move rule. It’s also sporting a shiny new user login system, allowing you choose your own user name and password, each up to 16 characters long.

Changes:

Added a custom icon to the ROM.
Added account handles and passwords.
Added account registration.
Added support for Castling.
Added support for En Passant.
Added support for 50 Move Rule.
Added status screen while the DS downloads a game.
Fixed a buffering error in the Client POST Handler.
Fixed checkmate detection. [No more victory on check. ;]
Completed the About menu option.
Local save games show when the last move occured.
Added screens after winning or losing a match.
Touched up the Online Games screen.
Touched up the Find Opponent screen.

http://www.armoredtactics.com/chessnet/?page_id=3