Hi Timothyd - first let me give an update. this functionality is not yet available and still in development. I wish I could give you a date; however, I don't have one. It is coming though.
For the question if Tivo will work with this Comcast function, it won't. Tivo does have a site which will work with the Tivo equipment.
This link
Watch TV Online at Comcast.net | Full Episodes | TV Listings | High Definition Videos is for Moto equipment with the Tivo software. It is available in the Northeast.
Not much help, but at least it may clear up some questions.