No S-Video is only video. The standard white and red RCA cables will take care of the sound. This assumes that sound is taken from the back of the soundcard output with a mini jack to RCA adapter. Although, thats probably not the best way. Just playing around with my video card, I used the S-Video out to a composite RCA cable to a VCR and the mini jack to RCA from soundcard to the VCR to record an AMV on a VHS tape. However, it looked and sounded like crap compared to me burning my own DVD. This is one way, but not the best for quality.
I believe most projectors have VGA/DVI input, so you could just get a two sided cable, thus increasing the quality immensly. And audio could be mini jack to mini jack (as far as I know). I've seen many ways of connecting a video source, but as for the audio, I think mini jack and RCA cables are about it for consumer level projectors. Higher-end ones might have digital coaxial or optical I think. However, connecting the sound to the projector would only use the internal speaker, which is crap. So get a seperate sound system to plug into for much better sound. I hope this helped. Heres some interesting links to read ^_^.
Do It Yourself projector for $300
DIY projector update