Vista - Another HDMI just dont understand

I hope someone can help, I have just brought a Media PC with a en9800GTX video card which has 2 DVI ports, I was told by the supplier that it is meant to be really good and do everything, I was also told when i got the machine that I really needed a HD TV with an HDMI port on the back so I had to go and get a panasonic TH-42PZ80B again being assured that this was what I needed. further to that I had to get a HDMI cable that would connect to the ports of the video card (via a hdmi to DVI converter) again being assured that this was everything I needed.
Picture quality is great but there is no sound! I can plug speakers into the back of the pc (green port with a standard cable) but there is nothing coming out of the TV, I have been told to right click on the sound icon in vista a change the audio to the TV but it is not listed!
Can anyone offer any advice please, the media PC was brought on the basis of being speced to the hilt but there seems to be so much conflicting information and nothing works! 4k down and seems that I have brought a donkey!

Who did you buy it from? Call them. Tell them to either get it working or refund your money.

I'm not experienced with all this side of set up...but my understanding is that DVI is video only and when using a converter to HDMI it means you won;t get sound through it.

You should have a red/yellow/white connectors on your media centre and your TV...try connecting those with the appropriate cables too... you should have sound then.

But I would have thought a Media centre would have a HDMI out connector to connect directly.

HDMI is HD sound and video. DVI is digtal video. You can use optical cable for digital sound. It would be the next best cable.

And, for future reference, don't rely on what you were told - Google is your friend, do the research yourself. You'll save yourself a lot of time, frustration, and headaches.