Apple Mini-DVI to Video Adapter. Apple's online store has it for 19 USD. Search for the terms "Mini-DVI to Video Adapter" and you'll find it. From the description:
"The Apple Mini-DVI to Video adapter is designed for use with the iMac (Intel Core Duo), MacBook, and 12-inch PowerBook G4. The adapter connects to the Mini-DVI port on these computers and provides both S-video and Composite video connectors so that you can view your computer on devices such as TVs, VCRs, or overhead projectors with S-Video or RCA (Composite) connectors. Video cables sold separately."
You'll need a cinch-cinch mono cable for connecting between the adapter to the TV set as well as a standard mini-jack to stereo cinch cable for the sound in addition. Like you'd use for connecting a portable CD-player to a home stereo.