I have a Tivo HD (Series 3) and use the Tivo Desktop software to bring the Tivo Files over to the PC.
.TIVO files are just MPEG with some encryption. You can use http://tivodecode.sourceforge.net/
and just rename the decrypted files .MPEG.
This is what I do. It works great. However, I do loose audio after about 10-15 mins of playing, but a quick stop/start fixes it for a bit.
If you have questions, let me know