I've just worked out a GENUINE SOLUTION TO THE missing ACPI kernel panic error.

Background:
on my intel macbook pro 2 GHz core duo, an update to Tiger 10.4.10 failed, with a grey "reboot your system now" screen.
upon rebooting i booted upto the grey apple logo screen, then a kernel panic error message was shown which indicated that the ACPI driver could not be loaded.
I tried reinstalling the OS using archive/install, resetting PMU, P-RAM, verbose mode, single user mode etc, none of which worked!

you will need:
an external HDD (or a CD-R *should* work)
your installation DVDs (mine were Tiger v 10.4.5)
the latest comboupdate DMG file from http://www.apple.com/support/downloads/
mine was called "Mac OS X 10.4.10 Combo Update v1.1 (Intel).dmg" approx 220 Mb of download!

Using a working computer, download the comboupdate file and copy it to the external HDD
On the mac with Kernel Panics, insert the install disk 1 and reboot, holding down the "C" key until you reach a language menu; choose english.
plugin the external HDD, and wait until you think the external HDD has been loaded.

select Utilities > Terminal from the menu at the top of the screen.
1) work out what where your internal and external HDD's have been mounted to:
type df -h
/dev/something1 -- -- -- -- /Volumes/My Book << this is my external HDD
/dev/something2 -- -- -- -- /Volumes/MacBookPro HDD << this is my internal HDD

2) mount the comboupdate DMG image; type:
hdiutil /Volumes/External HDD/MacOSXUpdCombo10.4.10Intel.dmg
3) where was this mounted to? type:
df -h
mine was mounted to /Volumes/Mac OS X 10.4.10 Combo Update v1.1 (Intel)
4) install the new update
/Volumes/Internal\ HDD/usr/sbin/installer -pkg /Volumes/Mac\ OS\ X\ 10.4.10\ Combined\ Update...pkg -target /Volumes/Internal\ HDD
5) if this finished successfully, exit terminal
Utilities > Startup disk > Choose the internal HDD and hit restart a few times.

success!