[iBook] Installed security update now iBook will not boot

[ibooklist2 at matthurst.fastmail.fm]

I had the same thing - updated my 3.9 G4 iBook, same vintage, and it
wouldn't boot. Since I discovered this on the way to a meeting round the
corner from an Apple Store, i took it straight in without fiddling
around, where they ran a Disk Warrior check. 

Apparently the header volume data on my boot disc was damaged, whatever
that means, so they did a quick archive and install on the OS X and now
it's all fine again. So maybe it's time for a quick visit to a genius
(personally they're why I find the Mac product so much better than PCs -
byte for byte, you might get more from a PC but 30 minutes in an Apple
Centre has saved me so much time, money and grief in comparison that I
know which is better all round value. Ad over).

They reckoned the most likely cause was a corrupted downloaded, or the
iBook freezing mid-patch. Since I'd left the iBook to sort itself out
over night, which is generally fine, I didn't know but it sounded like a
'these things happen' deal. I begin to wonder now though, since it's
happened to someone else.

Matt