Tivo offers a software solution called TiVoToGo that allows you to download programs from your TiVo to your computer. While this is nice, the downloaded videos include DRM which limits your ability to copy the videos and play them where you want (like on your iPod). There are some alternatives that offer similar functionality which allow you to copy from your TiVo to your computer but without attaching DRM to the videos.

For the PC: http://prish.com/etivo/tbr.htm

For the Mac: http://tdm.sourceforge.net/

Happy hacking!