here is the link to one of the way to play. I think there are other ways too:
http://www.menneske.no/sudokuto/eng/
anyway, here are the rules:
"The rules for inserting a number is the same as a regular Sudoku. You are only allowed to insert a number one time in the row, column or box.
The winner is the persons who either manage to fill in a whole row, column or box, or inserts the last legal number. But beware, you lose if you insert an illegal number."
Regards, Andy.