Well, a couple of things: the code I posted would only build the legend part, and it only works if you've already entered html markup in the usergroup manager to color code usernames by group. But assuming you've done that, create a new plugin using hook location forumhome_complete and this code:
PHP Code:
foreach ($vbulletin->usergroupcache AS $usergroup)
{
$usergroups[] = $usergroup['opentag'] . $usergroup['title'] . $usergroup['closetag'];
}
$usergroup_legend = implode(' | ', $usergroups);
Then in your FORUMHOME template, put $usergroup_legend where you want it to appear. When I tried it it came out fairly large, so you might want to put a <span>..</span> around it or something to control the font size.