I just finished a hard drive upgrade of my trusty Series 2 Tivo. I purchased InstantCake software from dvrupgrade.com for $19.99. It formatted the new high-capacity hard drive and installed the Tivo software on it lickety split. Took me longer to get the old windows PC out of the attic and set it up than the entire procedure including the physical drive replacement. Now instead of being limited to a maximum of 40 hours of recording (much less at best quality), I have 395 hours! No need to worry about watching stuff before it gets dumped to make room for more now.
I just love software that does what it promises — at a very fair price!