Thread: rca from computer?

I was reading in the car pc hacks book about eliminating the head unit and installing a touchscreen. In the diagram it shows a cable running from the carpc to the touchscreen (vga) and it shows a cable running to the amp from the carpc, (as well as from the amp to the speakers). Anyways my question is what kind of hookup am I gonna need to have to connect the amp to the carpc? Do i need to get a certain sound card with RCA connecters? Is there an adapter type thing I can get? Any help would be much appreciated.