I don't know if this is the "cleanest" way to query it, but it works for displaying how many posts have been made in the past 24 hours:
SELECT COUNT(*) FROM w3t_Posts
WHERE ( UNIX_TIMESTAMP() - B_Posted ) / (3600 * 24 ) <= '1'
You can change the 1 to a 7 for a week or 30 for a month.
