Index scan

Hi all,
I am unable to understand why my inidcies are not used in the query.
I have following indices:
index on categories.root
index on media.category
unique index on categories.id
Here is my query :
mondo=# explain select m.id
form media m, categories c
where c.id=m.category and c.root like 'B%';
NOTICE: QUERY PLAN:

Hash Join (cost=22.55..116.80 rows=11 width=28)
-> Seq Scan on media m (cost=0.00..60.40 rows=840 width=16)
-> Hash (cost=22.50..22.50 rows=20 width=12)
-> Index Scan using cat_id_root on categories c
(cost=0.00..22.50 rows=20 width=12)
EXPLAIN

I simply dont understand why it uses seq scan on media.
Thanks all for your help.
-Najm