Problems using count() with a join

Hi,
I have the following 2 tables:

Table groups:
g_id int4
g_name text

Table users:
u_id int4
g_id int4

What I want is to get a count of # of users in each group, even if there
are no users in the group.

I have tried the following:
SELECT t1.g_name,count(t2.g_id)
FROM groups t1,users t2
WHERE t1.g_id = t2.g_id
GROUP BY t1.g_name;

But it only give the counts of users in each group if there actually are
users in that group.
I want the count to be 0 if there are no users in the group.

Thanks.