I have one of those cables. I use it to connect my mp3 player (iRiver H120). This player has a jack line out that doubles as a optical out. That's why these cables exist.
So, like others have said, with your current sound card, you can't use that cable.
You have two choices now:
1. Return or sell that cable
2. Buy a sound card with optical output (if you have the toslink adapter)
I love optical, I simply can't resist holding the optical cable and point the light beam to the receiver optical in. This is my version of wireless sound transmission
