I finally got it !
I used the HDTV adapter cable I got with the 7300GS card to connect to the 9-pin socket.
(the 9-pin socket is very simular to the s-vid 4-pin connector, although it fits, you cant use the s-vid connector here)
I connected my yellow Composite cable to the GREEN
socket on the adapter and the other end to the TV's yellow composite in socket.
My screen on the TV turned black-and-white.
Now the sollution:
In nVidia Geforce 7300 GS settings I pick nView Display Settings, clone, click 1b (TV monitor), click Device Settings >>, Select TV format, Advanced.
Here I chose '(Combination) N/PAL' and 'Composite Video-Out'
Now I got NO picture
on the TV, so I switched the composite cable on the adapter from green
to BLUE socket
. And there.... COLOR TV!!
NOTE! There is a label on the adapter's cord saying:
Either use RED+GREEN+BLUE socket or
GREEN socket for composite
acutally you are able to use ONLY BLUE, but with S-VID and black-and-white screen