Constant Kernel Panics on startup on 10.4.7

Question

I had no problems after upgrading to 10.4.7 on my Titanium iBook so I upgraded on my G4 iMac desktop as well.
I had one successful restart under 10.4.7, but on all subsequent attempts, I've gotten kernel panics on startup. with a screen and a half of backtrade and exception state lines, filled with hexadecimal codes.?
Anyone else had this problem? Any suggestions as for how best to deal with it?
P.S. I did make a bootable backup of my disk before upgrading, and my first thought is that I should just restore back to 10.4.6 from the backup. The problem, however, is that the backup is on a firewire drive, and I can't figure out how to make the machine boot from the backup. Is there a simple 'button' trick I can use to make it boot from the firewire drive instead of from the internal HD? (Alternately, is there a way I can get my machine to recognize the Firewire drive from system 9.2.2. I have been able to contrive a way to reboot from the internal drive's 9.2.2. folder... but I can't see the firewire drives from it).

Answer 1

OK: Here's a follow-up:
I tried using the Startup Manager and, to my surprise, that didn't seem to help. It still wasn't recognizing my firewire drive backups as volumes.
I then went to Dr. Smoke's diagnostic list and looked through it. The first step that seemed both relevant and possible to my situation was the suggestion (through a link to a help page) that I reset my PRAM and DVRAM.
So, I went ahead and tried rebooting (in OS X) while holding down option-command-p-r, and the machine booted fine. No kernel panic at all.
I decided to try immediately rebooting into OS-X as per 'normal' (i.e. without holding down option-command-p-r). The kernel panic recurred. Several attempts at rebooting revealed the following: (1) Wiith each attempt to reboot off 10.4.7 on the hard drive while holding down option-command-p-r, I had no problems. (2) With each attempt to reboot from 10.4.7 on the hard drive without holding down option-command-p-r, I got a kernel panic. Hmm.... (That seems significant, but what exactly it means, I don't know.)
I did find out that, if I held down option-command-p-r while rebooting, I was able to boot successfully into 10.4.7 from the hard drive, and that from there, I was able to reboot into with no problem into 10.4.6 from my backup firewire drive (even if I didn't hold down option-command-p-r).
At this point, I'm planning just to restore 10.4.6 to my internal hard drive from my backup, and hope that works. (I'll post and let you know if it does.) However, if the information presented above suggests anything to anyone (e.g. about more specific problems that I should investigate, perhaps with the RAM, I'd be most appreciative to hear your thoughts.).