I'm not sure exactly what you are trying to do but here's my take on your problem.
If you just want to show a sorted list of the users that have more than 5 posts then log into your admin control panel, create a new widget of type 'PHP Direct Execution' and insert the following code:
$host = '<your host here>';
$user = '<your database userid here>';
$pass = '<your database password here';
$database = '<your database name here>';
$linkID = mysql_connect($host, $user, $pass) or die('Could not connect to host.');
mysql_select_db($database, $linkID) or die('Could not find database.');
$query = "select username, posts from user where posts>5 order by posts desc limit 0,10";
$resultID = mysql_query($query, $linkID) or die('Data not found.');
$output .= '<p>These users will be entered into the draw!</p>';
$output .= '<table>';
for($x = 0 ; $x < mysql_num_rows($resultID) ; $x++){
$row = mysql_fetch_assoc($resultID);
$szUsername = $row['username'];
$szPosts = $row['posts'];
$output .= "<tr>";
$output .= "<td>$szUsername</td>";
$output .= "<td>$szPosts</td>";
$output .= "</tr>";
}
$output .= '</table>';
After that just add the widget to whatever page you would like.
I'm not saying the code is bullet-proof but it should give you a start. In this example I am only returning the top 10. You can play around with the table to show all 500 if you prefer.
If I was going to code it up myself then I might either create a new table (or add a column to the user table if that's allowed) holding the baseline of everyone's post-count at the time you start the contest. Then if you wanted to see who has 5 new posts then you would simply subtract their baseline post count from their current post count.
Hope it helps... now if anyone wants to help me with my problem (https://vborg.vbsupport.ru/showthread.php?t=237243)then it would be very much appreciated!
-fab