Unfortunately, I can't tell which post will be number 200,000 since from the database's point of view, it's already been made (Ofour's last post in this thread is number 205,600). The discrepancy of around 8,000 posts is due to the deletion of double posts, double topics, and old forums (The Tavern alone probably accounts for 3,000).
For the countdown, you can always look on any of the forum index pages, then scroll down to the bottom where it shows birthday's coming up, who's online, etc.
EDIT: I love number crunching
It's looking increasingly that it'll happen between June 10th and June 12th, with June 11th the most likely possibility. June 10th is also somewhat likely, with June 12th being the least likely.
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