Maxcat: My advice; do NOT do the upgrade until you have emailed the Tivo Doctor - Darren who can supply a Tivo image and helpful advice to get you started.
Tivodr@gmail.com
I'm curious as to why you advise this.
I have upgraded both of my Tivos and each time I just used the existing image from the old HDD as a starting point.
Darren is obviously good to contact though if your old HDD is broken.
My advice to anyone who is thinking about upgrading their HDD when it breaks is to just upgrade to 2TB now and keep the old drive as a backup. The 2TB upgrade has to be the best $150 I've spent recently.