Search optimisation

I'm new to SQL databases although I've worked a lifetime on PICK type
systems.  I'm having trouble gettting selects to work well.

I have a database with a number of tables. I'm having a number of
problems one is this:

This query runs very quickly and returns one row:
select * from biblioitems where isbn='031051911X';
explanation:
Index Scan using isbnidx on biblioitems  (cost=203.35 rows=2988
width=102)

This is fast:
select * from biblioitems,items,biblio where biblioitems.biblionumber
='109' and biblioitems.biblionumber = items.biblionumber and
biblio.biblionumber = biblioitems.biblionumber
explanation:
Nested Loop  (cost=54.91 rows=657 width=340) ->  Nested Loop  (cost=4.08 rows=2 width=167)       ->  Index Scan using
bibitbnoidxon biblioitems  (cost=2.03
 
rows=1 width=102)       ->  Index Scan using bibnumidx on biblio  (cost=2.05 rows=59945
width=65) ->  Index Scan using bibnumitem on items  (cost=25.42 rows=73185
width=173)

This one is slow:
select * from biblioitems,items,biblio where isbn='031051911X' and
biblioitems.biblionumber = items.biblionumber and biblio.biblionumber =
biblioitems.biblionumber;
explanation:Hash Join  (cost=11830.17 rows=981357 width=340) ->  Seq Scan on items  (cost=4158.10 rows=73185 width=173)
-> Hash  (cost=5091.33 rows=2989 width=167)       ->  Hash Join  (cost=5091.33 rows=2989 width=167)             ->  Seq
Scanon biblio  (cost=2767.19 rows=59945 width=65)
 
             ->  Hash  (cost=203.35 rows=2988 width=102)                   ->  Index Scan using isbnidx on biblioitems
(cost=203.35 rows=2988 width=102)

How can I make this query use the indexes?