If your TiVo is part of a home computer network, this trick lets you watch PC-based files through your television, using the TiVo as a sort of digital media receiver. If you're so inclined, it's a little tricky to pull off but not impossible. Just make sure you have your TiVo box upgraded to software version 7.2.
You probably already have the TiVo Desktop 2.1 app on your PC, so just convert your video files to the MPEG-2 format, using a program such as Premiere or Nero, and stick them in the TiVo folder on your hard drive--usually in My Documents > My TiVo Recordings. After that, an entry for your PC-based files should be available through your TiVo. See, that wasn't very hard at all, was it?