It is unlikely even if he did find the answer it would help you since his post was from 2004 and for vBulletin 3.0.1.
That said the easiest way to add a quick image in front of a username for an entire usergroup is to go to the Admin CP -> Usergroups -> Usergroup Manager. Choose the usergroup and simply add <img> HTML code to the HTML Markup opening tags box.
There is limited number of characters so try to make the file path as short as possible.
Something like:
Code:
<img src="images/x1.png" border="0" />
Should work fine... the $nbsp; is so you have a small blank space between the image and the username.