Kevin (Tubedogg) actually came out with a Top 10 Posters script, that if you modify it correctly can pull off what you need.
If you go get that script, I think that changing this line :
PHP Code:
$postsresult = mysql_query("SELECT username,posts,userid FROM user $exn ORDER BY posts desc LIMIT 0,$maxposters") or die("Unable to complete query");
where it says posts (2 times) change that to referrerid .. then again it might not work... I might play with it later tonight... as soon as I get a couple of other things done.
Hard for me to test though, hehe I none of my ohh 10 members have refferals