JOIN exclusion problem

Hello,

I'm trying to join three tables, where I need only one piece of data from
two of the tables.  The code I wrote is:

SELECT apartner_nr, ap.anrede, ap.vorname, ap.nachname, ap.telefon, ap.fax,
ap.email, ap.kunden_nr, k.name1, ap.agentur_nr, ag.name1
FROM ansprechpartner ap, kunden k, agenturen ag
WHERE ap.kunden_nr = k.kunden_nr OR ap.agentur_nr = ag.agentur_nr
ORDER BY nachname"

The problem is that each row from each table is combined with each row of
the other tables.  I know the code is wrong, but I don't know how to write
it so that the results show only the actual value of ag.name1 and k.name1,
and not all of the possible combinations.

Is there a way of limiting how the rows are built up?  Pardon for novice
nature of this question...

Thanks in advance,

Anja