If you want to display images in the 8 subforum listings that you have here:
http://www.mknexusonline.com/forums/forum22/
Then I gave you the right code, but you are putting it into the wrong template.
If you only want to put the images in 2 of those subforums in the list (and I don't know why you would) then I still gave you the right code, and you still need to put it in the right template, but you also need to wrap it in a conditional to make it work that way.