Andre,
The way it seems to work is:
First of the month, BF assigns every member a random number between 1 and the current number of members. Mike opens a thread asking for a number between 1 and N posted after a given time. Mike T. takes the first number posted after that time, and looks up the member who was assigned that number earlier. As long as that member has made the required number of posts during the month, he wins, the contest is over. If that member has not posted, mike takes the next number in the post, and looks him up. As far as I know, no one has ever picked them self as the winner. You do not have to be on line at the time, or respond to the "I need a number" post to be in. I remember mike once sawing that he had to go through the first three or four numbers before he got someone who had posted during the previous month. Generally he tells us who picked the winning number.
Mike