Just thought I'd throw my hunk of script out there. The code's a little ugly, but it works!
Supports FLAC tags as well!
Preview:
$ifequal(%rating%,100,$char(9733)$char(9733)$char(9733)$char(9733)$char(9733),
$ifequal(%rating%,80,$char(9733)$char(9733)$char(9733)$char(9733)$char(9734),
$ifequal(%rating%,60,$char(9733)$char(9733)$char(9733)$char(9734)$char(9734),
$ifequal(%rating%,40,$char(9733)$char(9733)$char(9734)$char(9734)$char(9734),
$ifequal(%rating%,20,$char(9733)$char(9734)$char(9734)$char(9734)$char(9734),
$ifequal(%rating%,5,$char(9733)$char(9733)$char(9733)$char(9733)$char(9733),
$ifequal(%rating%,4,$char(9733)$char(9733)$char(9733)$char(9733)$char(9734),
$ifequal(%rating%,3,$char(9733)$char(9733)$char(9733)$char(9734)$char(9734),
$ifequal(%rating%,2,$char(9733)$char(9733)$char(9734)$char(9734)$char(9734),
$ifequal(%rating%,1,$char(9733)$char(9734)$char(9734)$char(9734)$char(9734),
$char(9734)$char(9734)$char(9734)$char(9734)$char(9734)))))))))))