SQL Help - Mailing list pgsql-sql

I am having trouble with the following query taking forever:
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SELECT * FROM ret108108_00, product
WHERE ret108108_00."isbn" = product."Item1"

AND   product."SuperCategory" = '1'
AND   product."PublisherCode" = 'ZON'
ORDER BY ret108108_00.qty DESC LIMIT 100
----
The problem is the second AND -- if I take this out it runs fine -- is there
any way to optimize it ?  I had a similar problem with just Category so I
created a new field in the product file called FullCat which combined
SuperCategory and Category and thus eliminating the 2nd AND clause -- and
that fixed it -- I just didn't want to do the same thing with Publisher.
Before I tried to index Category, SuperCategory ... nothing seemed to help

Any ideas

Thanks in advance
Mark Summers