My vaio is connected to my surround sound and from my surround sound to my 53" sony lcd. I've had my system set up this way for a couple of years now. It worked fine with vista and xp. I recently installed windows 7 and the sound was coming out of my computer instead of my surround sound. I was like ??? So I googled it and found a bunch of forums like this one with a lot of questions and no solutions.
SOLUTION: In my case, I had the sigmatel hd audio driver from the sony website installed.
-right click on the speaker at the bottom right of your screen and select "playback devices"
-you'll see that the hdmi is NOT detected (If you dont see HDMI then right click and select both "show disabled" and "show disconnected")
-go to "programs and features" (just press start and type it in the search box)
-in programs and features select the audio program and uninstall it
-go to control panel and select "device manager"
-scroll down to "sound, video and game controlers" and right click, then select scan for hardware changes
-Next, go back to the speaker on the bottom right of your screen, right click and select Playback devices
-Now it should recognize that the HDMI plug is connected. Just right click and enable it and set as default.

Good luck homies! :P
P.S. If you've never owned a vaio... DON'T!!!