Hi Max ... this may affect you then again it may not since I'm using a different TiVo (series 1 Sony SAT-T60) than you, but here's what happened to me... I used the InstantCake CD to upgrade my Tivo and used a 160GB hard drive, bigger than 137 GB in other words... then I think Tivo sent out a "c" upgrade" over the telephone line to my TiVo the next time
TiVo did it's Daily Call (b.t.w. I had to try several times to get my Daily Call to work after my InstantCake upgrade but it did work eventually)... after that I noticed a problem recording shows, sometimes TiVo would record a show okay and other times it wouldn't, the TiVo unit would reboot (power off then power on again) right in the middle when I was watching a recorded show... so then I went to this website:

http://www.ptvupgrade.com/support/bigdisk/

downloaded the LBA 48 ISO upgrade mentioned there, burned it onto a CD, re-attached my new TiVO hard drive to my computer (for some odd reason I found that the new hard drive has to be attached to the secondary master, not the primary master, IDE drive in order to get either Instantcake or the LBA 48 upgrade to work), booted off the LBA 48 CD I created, and ran the copykern command the CD mentions (once you boot off the CD it will give you instructions on how to complete the copykern process)... Also please note that I did not have to run InstantCake a second time on the new hard drive before doing the LBA 48 upgrade and I also did not lose any of my recorded shows, season passes et cetera after doing the LBA 48 upgrade.... I haven't had any problems since then though knock on wood here, I only did the LBA 48 upgrade a couple of days ago (July 26th) so I'm going to have to wait a few weeks to see if this really solved my problems (the rebooting right in the middle of watching a recorded show I mentioned happened a few weeks after I'd upgraded my TiVo)...

Now depending on how recent the version of InstantCake is that you ordered you might not even have to do the LBA 48 thing... according to Lou (the InstantCake guy who posts the "official" InstantCake replies in this forum) recent copies of InstantCake should contain the LBA 48 software upgrade... I know that I ordered my InstantCake CD back on July 4th (fairly recent) and still had problems 'till I did the LBA 48 upgrade...

If the ISO / creating a bootable CD thing is confusing at all, check out this link which talks about how to create a bootable CD from an ISO image ... http://members.home.nl/lsnoek/iso.htm .... hope that helps!...