Here's the query....
SELECT Count( * ) AS UserPosts, POST_POSTER_NAME
FROM ubbt_POSTS
WHERE POST_POSTED_TIME > UNIX_TIMESTAMP( CURRENT_DATE ) -86400 *30
GROUP BY POST_POSTER_NAME
ORDER BY UserPosts DESC
LIMIT 60
replace 30 with the number of days
...and 60 with the total number wanted on the list.
I think Rick provided me with this code