I have tried connecting my Dell Studio Laptop to my Sony AV through the laptop's HDMI port, I get video but no sound. The only way I can get sound is through the headphone jack on the laptop.
Anyway, usually..you should see and HDMI(audio) device listed in the Control Panel sound options after making such a connection. Just chose that as the default playback device. If on Win7, you might have to right click>show disabled devices in the playback devices window.
I have tried connecting my Dell Studio Laptop to my Sony AV through the laptop's HDMI port, I get video but no sound. The only way I can get sound is through the headphone jack on the laptop.