say you have a forum called "ps3", in the forum prefix box add the prefix "ps3_" (without quotes) and then get your icon and call it ps3_forum_new.gif and upload it to images/statusicon
you I have images for locked and old,
so what I have done is have the same image set to grey scale and call it ps3_forum_
old.gif
also add a small padlock img and call it ps3_forum_new_
lock.gif
and so on...
that should work!
check out my clans new forum here as I have done it with sub forums also!
http://www.manchesters-armed-defenders.co.uk/forums
Dan