There are many posts on the forum about checking if the user is logged in or is an admin/moderator.
However is there a way to see if a user is in a secondary usergroup?
Well it depends on a couple things:
Can that group ever be a primary group?
Do you want to exclude those who have that group as a primary group (if it can be primary)?
If the first is false (ie it can never be a primary group) or the first is true and the second is false then you can just use:
in_array(##, $user_info['groups']);
If the first is true and the second is true then you'll have to do a query
$res = db_query("
SELECT ID_MEMBER
FROM {$db_prefix}members
WHERE ID_GROUP != ##
AND ## IN (additionalGroups)
AND ID_MEMBER=$ID_MEMBER
LIMIT 1", __FILE__, __LINE__);
if ( mysql_num_rows($res) == 0 )
die("Go away you");
mysql_free_result($res);
Thanks