To change icons or different forum icons for each forums, you can use CSS solution only by Glenn in post no 4 here:
vb5 temp fix for custom forum icons(any size) - vBulletin Community Forum
http://www.vbulletin.com/forum/forum/vbulletin-5-connect/vbulletin-5-connect-questions-problems-troubleshooting/vbulletin-5-tutorials/4028327-vb5-temp-fix-for-custom-forum-icons-any-size
big thanks to Glenn Vergara (http://www.vbulletin.com/forum/member/326711-glenn-vergara) for this code...now we dont need to wait for a custom sprite editor to get