I just finished (finally!) updating my TiVo with a 160 GB drive I found at CompUSA for just $30 after rebates. I bought it a couple weeks ago, but got frustrated with it after messing around for a couple hours. You have to take an image from the original drive(s) to get the OS and settings, then write the image to the new drive. I was having problems getting my machine to recognize the two TiVo drives so I could pull the data off.
If you want to do it, the directions are available online, but don’t follow them word for word. I couldn’t get my machine to recognize the drives in the configuration they recommend - most of the commands were different, since the drives weren’t attached where the author’s said they would be. I learned a few things about Linux mounts in the process though, and it all worked out.
We now have a TiVo with lifetime service and 45 hours at best quality - 160 at basic. And BP just bought a big TV a couple weeks ago - what more could a man want?