[Kirk Y]

If you want a no frills version...

Create a new plugin using hook location "global_start" with the following:

if (in_array($GLOBALS['forumid'], array(2,5)))
{
$stylevar['titleimage'] = "/images/forum_".$GLOBALS['forumid'].".jpg";
}

Then simply change the numbers in the array to the Forum IDs you'd like to have custom logos displayed; and move the custom logos to your "/images" directory, renaming each to the following: forum_X.jpg - where X is that logo's Forum ID.

Any Forum ID you don't specify in the array will use the default logo.