TinMan55:
I had an idea - being that the Tivo was not recognising the additional space on the new drive, I restored to it from the truncated backup I had taken of the original drive using Winmfs, selecting the option to add the extra space. Now, firing up the Tivo on the big drive, the extra space is there (says 400hrs), but although all of my recorded programs appear to be there, some of them have only the title, and clicking on them says there is nothing recorded. I have to say that I suspected not "seeing" the extra space wasn't the only thing lacking, as the copy had carked about two-thirds through; i.e. not just at the final step. So it looks like my options at the moment are-
Keep the original 320GB drive installed (which is full) so I can watch the stuff on it, while recording new stuff on my second box.
or -
Just go with the new bigger drive and accept the fact that some of the recorded stuff is lost (a higher authority may rule on this!!)
or - try and figure out how to drive JMFS to successfully clone the drive fully.
If the drive is anyway faulty - your more likely to strike it while imaging the system with all your existing recordings - many applications have problems with drives with surface issues. ddrescue is probably the best application for coping a potentially faulty drive - it skips past bad sectors getting most of the data off first them coming back around to get the what it can from the bad areas of the drive.
If you feel comfortable here is a guide on using ddrescue with a Tivo:
http://www.logicsector.com/tivo/how-to-clone-your-failing-tivo-drive-with-ddrescue/
However instead of using the distribution mentioned in that guide I would use a spare USB Drive, and download http://www.system-rescue-cd.org/Installing-SystemRescueCd-on-a-USB-stick/ following the install instructions under C)
Alternatively I'm happy to do this for you at no charge - you would need to leave the original drive with me for a few days for ddrescue to run and do its thing.