Hi, does anyone know if I purchase a Comcast DVR on ebay will I be able to use all the DVR features? Right now I have Comcast Digital cable with an HD box, can i swap it out or do i have to call comcast?

No, Comcast or any other cable company will not allow you to use a cable box that you purchase yourself. STB manufacturers do not sell these boxes directly to consumers in the US. The boxes on ebay are either stolen or from Canada where they are sold directly to consumers.