How are messages ordered on the board?
This is very simple - whenever a message is replied to it goes to the top of the board. If no one replies to a post it will eventually ‘fall off’ the front page of the board, at which point it can be considered pretty much dead.
Often you will see a reply to the post which just says TOP (or something similar) - this means that the person who posted it just wanted the thread to go back to the top of the message board to ensure more people read it.