This is a discussion on Comcast MyDVR - Setting my DVR to record from the web? within the Comcast forums, part of the Cable and Satellite Providers category.
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.
This was always a plus for DirecTV and one of the reasons why I went with them. The day Comcast gets this feature online and working just as well as DirecTV's online scheduling is the day I'll seriously think about coming back to cable.