Upgrading a TiVo Premiere or Premiere XL to 2TB and 317 hours of space is quite easy thanks to the jmfs tool by Comer of the TiVo Community. So I upgraded last week. It took 7 hours just to copy the data, but it was worth it. My TiVo went from always on the edge of full to 48%!
Here is how to do it without a CDROM drive or Windows machine.