All the brand new "Holiday Edition" Tivos on Trademe are old stock with either purple or white stickers on the box explaning that the offer has expired. Otherwise it's around $129 or you won't be able to get recorded items on or off your Tivo and onto a PC.
I use the free Java based program Kmttg (Google it. It may well work on a Mac also) to get stuff off my Tivos, and the excellent Vuze as mentioned above to transcode mkvs and Avi's etc which become available automatically in the Tivo's "Now Playing" list. You select the show you want to view and the Tivo copies it to its HDD and you can then start playing it within seconds, as it copies. I believe the Tivo Desktop isn't a great piece of software but I haven't tried it personally.