Regardless which setup you are using, if you want to limit it just to a single usergroup find line:
After
Add
Code:
$usergroup_limit = 6;
Find
Code:
WHERE ".TABLE_PREFIX."customavatar.visible = 1
Replace with
Code:
WHERE ".TABLE_PREFIX."customavatar.visible = 1 AND ".TABLE_PREFIX."user.usergroupid = $usergroup_limit
Now just change the usergroup_limit number to match the usergroup you want to display. 6 for example is Administrators.