If they know the link to the chat, just using a template conditional to hide it won't work. You'll need to have the 'misc.php?do=page&template=Chat' do a check on usergroup. For example:
PHP Code:
if ($_REQUEST['do'] == 'page' AND $_REQUEST['template'] == 'Chat')
{
if (!is_member_of($vbulletin->userinfo, 2,6,7,38))
{
print_no_permission();
}
}