Also see here: http://www.chess.com/groups/view/capture-the-king
And here's a new rule:
After one side captures the opposing king, if the other side can immediately also capture the opposing king, then the game is a draw.
Example:
e2-e4 e7-e5
f2-f4 f7-f5
d1-h5 d8-h4
h5xe8 h4xe1 draw!