let's go over some basics.

The "Red White and yellow ports" are the "composite video" and the "Stereo audio" connectors on your TV. The yellow one is Composite video. The red and white ones are just stereo audio (each one of them will do one side of the sound, so if you've only got one plugged on you'll only hear one side). Don't confuse composite with component (which is 3 connectors that all carry parts of the video signal).

In order of video quality, pure component video is the best (but also the most expensive). Pure S-video is second-best. Pure composite is third. Going S-video to composite will probably get you in somewhere slightly behind where you'd be if your video card did straight composite output, but there's not much you can do about that.

As Haku said, you'll need an adapter. Go to radio shack, tell them you need an s-video to composite adapter (or just s-video to RCA they'll understand too). If it's not long enough to reach your tv you'll need a composite (NOT COMPONENT) video cable too. That ONLY handles video, and you'll need to get the audio from your soundcard with a separate cable. That'll end up plugging into the yellow connector on your tv, leaving the red and white ones free for a separate audio signal to come in.

For the audio, you want a "headphone jack" or "mini-headphone jack" to RCA Y-adapter. It'll take your stereo output from the headphone-sized jacks on the back of your sound card (same place as you plug your speakers into) and split it to the sound inputs on your TV. Again, radio shack is your first, best line of defense.

If your sound card only has one sound output and you want to use multiple things (ie: the TV and/or an output to your speakers or your stereo or whatever), you may need to get a splitter for that, too. Look at what you have, make sure you know what stuff does on the back of your computer, write it down or draw it, or both, or take a picture, whatever. If you're not sure, ask the people at the store you're buying it from. Explain what you want to do and what you've got. Maybe have them draw you a diagram for how you're going to want stuff set up. Be aware of what they try to sell you though.... some people at electronics shops try to sell you hundreds of dollars of stuff with extra features that you don't want or need, when all you need is 3 cables. In this case, all you need is 3 cables. Maybe 4 or 5 and maybe a $15 audio splitter.