David Howe wrote on Sun, Sep 29, 2002 02:30 PM UTC:
Here's the rule from our FIDE laws page
(http://www.chessvariants.com/fidelaws.html):
10.10
The game is drawn, upon a claim by the player having the move, when the
same position, for the third time:
(a) is about to appear, if he first writes the move on his scoresheet and
declares to the arbiter his intention of making this move; or
(b) has just appeared, the same player having the move each time.
The position is considered the same if pieces of the same kind and colour
occupy the same squares, and if all the possible moves of all the pieces
are the same, including the rights to castle [at some future time] or to
capture a pawn 'en passant'.