[ForumDog]

Give your background image the same name as the forumid for the forum with which you want it associated, then in forumhome_forumbit_levelx_post find:

<td align="left" id="f$forum[forumid]">

and either add a CSS class to it or otherwise inside the tag add:

style="background:#fff url($stylevar[imgdir_misc]/$forum[forumid].jpg) right center no-repeat;

Which is roughly what you want to do I assume, that's what I used inside the forum section with a large image for the background and a smaller one as an icon since I think you can use the same conditional in most of the major locations, i.e. http://doghouse.forumdog.com/forumdisplay.php?f=54