Is this a R
Is this a Roamio? If so, you can capture and store the current programs on an external PC using the TIVO desktop plus program:
http://support.tivo.com/app/answers/detail/a_id/1202
This used to be free, but they now charge for it.
Putting a 2 TB drive in a Roamio is trivial. Just plug it in and it formats itself.
If you have the older Premiere, you need to format the disk externally. There are programs available at TIVO community or there is some guy there that will sell a pre-formatted 2 TB disk.
Oh yeah, put in the 2 TB disk before the guy gets there with the cablecard. Some of the pairing data gets stored on the disk and people report you may have to re-pair if you change HDD.