Ah, yes I am starting to see the light, thanks. This seems to work:
select
m.group_id,
g.group_name
from
group_approved_member_map m,
groups g,
acs_objects o
where
m.member_id = :customer_id
and o.object_type = :customer_group_type
and o.object_id = m.group_id
and m.group_id = g.group_id