10.4.7 update ate my MacBook. Any suggestions?

Question

I just tried to install the 10.4.7 update via "Software Update" and:
1) The update failed (it reported an "unknown error" and put the installer in the trash).
2) The system became unstable after that, in particular the Finder and Firefox wouldn't respond.
3) After a hard reboot, the system won't start.
I've run Disk Utility from the install DVD and repaired permissions (two were repaired) and verified the disk (no errors) and specified it as the startup volume (just in case). From the intall DVD's Terminal.app I can go in and see my files.
I've tried several times, with both hard and soft restarts, and it's always the same: I get the grey Apple, I get the spinning spokes, it stays like that indefinitely (max 20 minutes or so thus far before I gave up).
So, I'm pretty confident there is nothing wrong with the hardware, and my files look safe, but it does appear that the 10.4.7 update is going to cost me the rest of the evening.
Any hot tips or suggestions?
My obvious next step is to reinstall the software, which of course is a giant pain, not least because of the fifty terabytes of system updates issued in the last two months. So I'll try just about anything else...
I have another Mac I can use to get at it (perhaps via Firewire) but the second one is a PowerBook. Also, I can get into the terminal fine from the install DVD.
The only unusual thing I can think of as a contributing factor is that I was copying some large files from a DVD while the update was downloading, and it may have gotten confused trying to install itself while the Finder was busy.
Anyway, here's hoping some kind expert will give me the secret inside tip. 'Cause today it feels just like when I use Windows at work...
(Oh, and yes I realize that the obvious obvious tip is to do a full system backup before installing a system update, what can I say, I was lulled into a false sense of security.)

Answer 1

Well, since I have to either get this working or give it to Applecare tomorrow, I decided to try to reinstall. Ouch.
However, in Googling around since then it sounds like there might be some hope for applying the update in "Target Disk Mode" which, IIRC, is with your Mac tethered to another Mac via Firewire. But I imagine they both have to be Intel Macs, which leaves me high and dry anyway.
But if you have another Intel Mac handy, it might be worth a try.
Meanwhile I noticed another thread from someone who had a very similar problem with 10.4.6:
http://discussions.apple.com/message.jspa?messageID=2069439#2069439
Looks like the same problem I had; didn't look like he got anywhere with it.
Also, another thread had this link which was useful knowledge in retrospect:
http://www.macfixit.com/
...to which I would now add, "do a FULL backup to an external drive, using SuperDuper or something like it, before even looking at a system update."
Which is funny, because giving advice like that is exactly what makes my non-Mac-using friends sneer.
Oh, and re: contacting an Apple employee... I agree but this is, um, the Apple company support forum, so I'm sure someone in Cupertino will read it ASAP and escalate or ignore the problem as they see fit.