How to connect PC audio to an hdtv?

Im helping my friend out he wants to connect his desktop to his hdtv, im using a rgb cable to connect to the hdtv but how would i wire up the sound card to the audio input on the tv, the red and white rca cables found here are what would normally be used to say connect my cable box to the tv, but since the sound card on the desktop has a smaller output, what would i use to convert the connection in order to get the audio.
BTW: he has a vizio vx37l

thanks so much, i tried searching for that product at monoprice but i had no luck, would it be under something else, bc im ordering an hdmi cable from there so it would be easier to order everything from the same place

thanks alot guys i really appreciate the help