4
since most web forums utilize a similiar look - I'd start by looking for existing modifications and themes for other forums.
PHPBB:
http://www.phpbb.com/phpBB/catdb.php?db=2
http://www.phpbb.com/phpBB/index.php?c=6 <-Styles Release forum
Invision Power Board:
http://www.invisionskins.com/
Does anyone else have good links for graphic sets (avatars, rank images, forum graphics)?
If planning on re-releasing any derivative works, it is a good idea to contact the original author and getting permission.