Using dvi and audio

Hello,
I have a LG 42PZ61 installed into the place I've moved into, and I've placed my desktop PC close to it. I'd like to be able to get sound and video to both the computer and TV. The TV does not have HDMI, but it does have DVI. I can plug that in and it looks great. Because the computer's sound plug is a female headphone sort of one (3.5mm?), I bought a splitter and 3.5mm to audio cable (the red/white), and there are plenty of spaces to plug those in, but none of them produce sound when the TVs input is set to "DVI." I can set it to Video 1 (or whatever) and can get sound, or I can have video through DVI?

What do I do? Do I need another cable, like a female DVI to male composite or something??

This problem is driving me bonkers!