S-video cable is stricly for picture only.
I'm not sure about the sound card you have ,but assuming you have a choice of 4 speaker mode in creative audioHQ.
Turn 4 speaker mode on in your creative speaker settings.
Now all you have to do is connect a mini Jack lead to your sound card (beside the other speaker cable), This lead should have a red and white end on it like the one on your tv.
Your tv should have red and white (rca) ports on it,beside the svideo connection.
Don't be afraid to ask for a mini jack to rca(phono) lead in any sound store and play around with the leads until you get what you want.
If i buy anymore of these leads i think i'm cracked