top poster during certain period of time

[kh99]

I think this should work:

SELECT username, COUNT(*) as count FROM prefix_post 
WHERE dateline BETWEEN UNIX_TIMESTAMP(YYYYMMDD) AND UNIX_TIMESTAMP(YYYYMMDD)
   AND visible = 1
GROUP BY userid
ORDER BY count DESC

(of course you have to insert your own table prefix, and the dates you want in place of the YYYYMMDD)

ETA: ...and you probably need "AND visible = 1" in there to eliminate deleted posts (so I went ahead and added it).