How can I record the sound of a s-video source, as when I display it there is no option in TVCenter to select the audio from line input of the sound card ?

Welcome to the forums jpnn80,

S-Video is video only. Use the 3.5 mm audio port for audio.

To be specific.  Are you saying connect a cable from the vidoe out source to the 3.5 mm audio port on the A/V Adapter that attaches to the stick?  I am doing this and still not getting sound.  I also notice that when I go to the Audio Configuation, Analog audio input, I cannot change the 'Installed TV Tuner Hardware' to PCTV HD Ultimate Stick S-Video.  I can select it but it does not stay.

The AV cable let's you use either S-Video or yellow RCA for Video. You still need to connect the Red/White RCA for Audio. When you set S-Video or Composite on the settings, it automatically looks for audio signal from the Red/White cables.