Audio From Graphics Card?

As far as I know, you can only get audio via HDMI. The drivers for it should be installed when you install the video card drivers. Should be as simple as connecting the DVI-HDMI adapter and the HDMI cable to your computer and monitor/TV.

I'm running my 3870 this way to a 42" LG LCD, works beautifully

You may run into some issues on the way though, no sound and the such. If you have problems with the sound, read this:

http://www.tomshardware.com/forum/ [...] adeon-3870

On an alternate note, if you're on vista, to make sure the sound is working, go "Control Panel" --> "Sound", and check which devices are working. You'll want the HDMI as your default, and that it is labeled as working. If you don't see it, right click in that window, and make sure "Show Disabled Devices" is checked off, as it might be hidden. Beyond that, you might have to go searching the net for the RealTek driver. I'm not sure where to look for that, but I'm sure other people do.