[Dave]

So you want to remove the threads and posts but leave the post counts of your members as they are? If you simply remove the threads/posts with SQL queries straight out of the database, it will not have impact on the post count.

Although I believe that if you do it straight in the AdminCP, it should not recount the post counts either.

Just keep in mind that whenever you execute the "Update Post Counts" function in the AdminCP > Maintenance, it will obviously update all the post counts and update it to reflect the actual number of posts users have made.