Video cards with HDMI outputs don't send audio signals.
Something like this can be used from the headphone jack to the receiver/TV:
http://ecx.images-amazon.com/images/I/41JGQR4TJML.jpg
If your TV doesn't have a VGA input, you could buy one of these for like $3, plug it into your computer, and run an S-Video or RCA cable for the video. This sends an analog signal, not the greatest for high definition video:
http://www.camerapartsmall.com/pro_images/157.jpg
If your computer only has DVI outputs (no HDMI) and you want the best picture quality, I would go this route. These send a digital signal and support everything out there:
http://www.visionhd.ca/images/dvi-hdmi.jpg or http://www.konecable.com/ZenCart/images/hdmitodvi.jpg