Performance question

Hello,

I have ported a database from MS SQL Server to PostgreSQL.  The database has
40 tables and 117 indexes which I defined for the same fields as in MS SQL.
I converted the data using some SQL output from MS SQL server and inserted
it with psql.

Now I started some performance comparisons and did the following statement:

SELECT Hauptdaten_Fall.MeldeKategorie, Count(Hauptdaten_Fall.ID) AS Anz
FROM Hauptdaten_Fall
WHERE (((Hauptdaten_Fall.IstAktuell)=20))
GROUP BY Hauptdaten_Fall.MeldeKategorie
ORDER BY Hauptdaten_Fall.MeldeKategorie;

(sorry for the German names used here).

The MS-SQL server represents the result "immediately" - you just not notice
any delay.  If I do it on the PostgreSQL server it takes 30s on comparable
hardware :-(((.

I really have no idea what caused this big difference in speed which would
forbid the use of PostgreSQL for our application.  How can I checked
whether the indexes I created are really used?  What could be other
reasons for such a big difference in speed?

I´m using PostgreSQL 7.1.2 on Debian GNU/Linux (testing).

Any help appreciated

        Andreas.