See ErcExtraModules first if you use the version of ERC that comes with Emacs 22 and you don’t have erc-chess.el.
erc-chess.el allows you to use ChessMode to play chess over IRC.
CTCP is used as transport protocol, and standard SAN move notation. So in theory, other clients could implement the CTCP CHESS command too. Currently, only ERC supports this.
You need to load erc-chess somewhere in your startup files, or do M-x load-library RET erc-chess RET. Please note that the library needs to be loaded if you receive a match request. If it isn’t, it will not work.
Then, simply use the command /chess <NICKNAME> to send a chess match request to someone.
Sounds neat! But where is the link?