SELECT performance problem on a join

Hello,

I have a great problem with performances of my database, on the SQL request:
---------------
select t_test.doc_id,  t_test.f_num_centre, t_test.f_num_candidat from
t_test, doc where t_test.doc_id=doc.id and doc.docsubset_id=2000077392
---------------
The doc table has 36.000 rows, and t_test the same. There is an index on doc
(docsubset_id) and an index on t_test (doc_id). There is others index too.

When I send this request, I must wait for about 45 sec. before the results
appears.
The server is a BI-PII 266, and there is about no activity on the database
neither on the server.

When I was using this request under MS-SQLServer (v6), the wait time was
about nothing.

What's wrong ?

Thank's a lot
Patrice Espie