That's right the 1000th post wins, but for the win to count you have to claim it in the 1000th post. something on the line of this is the 1000th post and I won or some such similar nonsense.
If the owner of post 1000 doesn't claim their win, the game stays open until the 2000th post and so on.
I'd rather the posts made some kind of sense, even if just in a string of random thoughts way, but I'm not an administrator and can't enforce that rule.
As with the rest of the forums here, the only thing the winner gets is bragging rights