This is what I recommend:
Set up your Premiere through the guided setup and get the cable card paired.
Make sure the Premiere has downloaded and installed the latest software (should be 220.127.116.11).
Get a 2TB hard drive.
Click the following link and start reading.
This software will copy your Tivo hard drive and increase your recording space.
Once this is done, put the original hard drive on the shelf for safe keeping because if the new hard drive ever goes south, you will have a backup that you can use to either make another copy or install in the Tivo for emergency TV viewing.