Yes, that will let you output video via either S-Video or composite video to your TV.
However, if your TV has a VGA input I would suggest using that instead as you will get a better picture quality. Apple also makes a mini-DVI to VGA adapter for the iMacs that would allow you to do this.
As for sound, it isn't that hard, you just need one more cable. You can pick up 3.5mm to RCA audo cables/adapters for about $5 at RadioShack that will allow you to output the sound from your headphone jack to the RCA plugs on your TV. Done!
Possible other option for audio:
If you have a newer MacBook that has optical audio out (it is hard to tell since optical out was combined with the headphone jack) AND you happen to have a high end TV with optical audio in (most have out but not in) then an optical audio connection would be a possible alternative. This would give you slightly better sound and the optical output allows for more than two audio chanels if you your source has that and you have the speaker system to output it. However, the cable is a little more expensive, harder to find and won't give you noticable improvement to sound if you are using solely your TVs interal speakers.
