You don't need TV out, you just need compatible inputs and outputs on your TV and your Video card, as your HDTV can just function as a monitor. Most HDTVs are plug and play. Also make sure you use a resolution compatible with your monitor, particularly if the TV is plasma as those are rather finicky with resolutions.
If your HDTV has an RGB or DVI input and your video card has those outputs (they always have one or the other), use either of those instead of S-Video, as the quality will be far better. Also remember you'll need to hook up your PC to speakers to hear anything.
If it's a laptop, there is usually a function button that allows you to change screens by pushing it and the corresponding F-key. If not, check display properties for different monitors and select your HDTV.
If the image looks messed up it's probably a resolution issue. Change resolution until you find one that looks good, but remember to use resolutions compatible with the TV. They'll be listed in your TVs manual or just google the model number.
Hope it works out, if you have problems post the models of your TV and your video card.