If the video / movie files you want to view are in a format that is not supported by the Apple TV system, you may be able to convert them into a compatible format with Video Converter Pro for Mac.

Apple TV is a digital media receiver manufactured, marketed and sold by Apple. It is a small form-factor network appliance designed to play digital content originating from the iTunes store, YouTube, Flickr, MobileMe or any Mac OS X or Windows computer running iTunes onto an enhanced-definition or high-definition widescreen television.
Apple TV can function as either a home theater-connected iPod device or a digital media receiver, depending on the needs of the user. It was first announced at a special press event in San Francisco, California on September 12, 2006, by Apple CEO Steve Jobs. The devices started shipping on March 21, 2007. This initial version shipped with 40 GB of storage. A second version with a larger 160 GB hard disk started shipping on May 31, 2007.
Apple TV is a network device that allows consumers to use an HDTV set to view photos, play music and watch video that originates from an Internet media service or a local network. Internet media services include the iTunes Store, YouTube, Flickr, or MobileMe. By connecting directly to the iTunes Store, users can buy and rent movies, buy television shows, songs, albums, and music videos and subscribe to video and audio podcasts, much of the content in high definition. Consumers can browse and view YouTube videos and Flickr or MobileMe photo albums. Apple TV can also sync or stream photo, music and video content from a network-connected computer running iTunes. Apple TV includes enhanced remote control and AirTunes capabilities.
Apple plans to continue offering new features through automatic software upgrades, leaving the door open to further utilization of its hardware capabilities and new software developments.
DVD to Apple TV Converter for Mac is an easy-to-use Mac DVD ripper software to get movies onto your Apple TV. It helps you convert DVD content to Apple TV MP4 video with high-definition and 5.1 surround sound. The converted MP4 video can be used for playback on your Apple TV. Also, the video files can be used for video editing.

(PC user? Get Windows version here)