THANX a LOT to Al for this guide

First, encode your videos to MPEG2 format /.mpg/ with MPEG2 Works 4 like you normally do. Your TiVo will not properly recognize any other video formats, including MPEG-1 and MPEG-4... MPEG2 encoding tutorials are located here:

.mov > MPEG2 /encoding your movies to MPEG2 and authoring
.wmv /Windows Media Video/ > MPEG1/MPEG2
DivX, XviD, AVI > DVD How-to...

Then, download and install the TiVo Desktop software, which lets you stream your iPhoto library and your iTunes music to your TiVo. TiVo Desktop doesn’t give you any video functionality, so you’ll need to enable its hidden video transfer feature. 
First click the Stop button in System Preferences > TiVo Desktop. Launch the Terminal (located in /Applications/Utilities/) and type:

defaults write com.tivo.desktop FileVideo -dict-add VideoUIEnabled -bool true

Reopen System Preferences > TiVo Desktop, and you’ll see that a new Videos tab has appeared. Check the box to publish your videos and choose the folder that has your MPEG-2 videos in it. Note that before you click the Start button, your MPEG-2 videos /.mpg/ must already be located in your chosen folder. If you decide to add more videos to that folder later, you’ll need to stop and start TiVo Desktop again for it to recognize your new videos.

Finally, on your TiVo, scroll all the way down to the bottom of your Now Playing List, and you’ll see your Mac listed there. Choose the videos that you want to transfer, and TiVo will transfer the movies into your Now Playing List so they’re available even after your Mac is turned off.