@samosa:thanks for ur help.
OK.to make things clear,the small wire that is supplied is to be used between tv tuner output(

) and onboard/soundcard input.
and t
he STB provided by sun dth has the normal A/V output and it is the pinnacle pctv 50i which is not having audio input as the pin is different! afaik.
and line-in is already selected and now he is watching TV using as follows:
1.S-Video from STB given to S-Video input of Tuner card
2.audio o/p from audio out(same pin as the headphone one) of STB is plugged into line-in of onboard soundcard.
3.with this settings,he is getting sound playing always,I think(heard via phone!)

and yes line-in is used.
and regarding the small cable to be connected between Tunercard and sound card,the small cable(i havent seen it yet!) has got pin types which are different at both ends and the technician is going to get a cable that fits both ends!
I have literally tried my best by explaining via phone for over an hour(

) ,he can hear sound and watch videos which are crystal clear(acc. to him).
but if he tries "Capture" feature,video got recorded,but audio is left !
and worst of all,a new Rs400/- frontech soundcard is lying there without any use