I recently went through hell to get OS X installed on my Dual G4 450. Having read most of the public message boards (macfixit, macnn, apple, macaddict etc) looking for answers, I thought I would impart some of my hard won knowledge to the greater readership of macosxhints.
If you are getting kernel panics or installer error messages that say "could not write file to disk/archive" during your install, you may have problems with RAM or 3rd party devices.
For more great installation tips from Yuri, read the rest of the article!
To give your install the best chance of success do the following:
Remove all RAM that is not factory installed! Many people are having problems 3rd party RAM even WITHOUT installing the firmware updates and even though their RAM has worked for months/years under OS 7,8,9 and the Public Beta.
Disconnect all third party hardware including all non-Apple PCI cards (e.g. SCSI cards, video cards) USB, and FireWire devices.
If you have a Beige Mac, make sure your installation is on a partition/volume that is within the first 8 gig's of the drive, preferably the first partition.
I would strongly recommend that you backup your entire drive before you attempt your install and partition your drive into at least 2 working partitions before installing (minimally one for OS 9.1 and one for OS X and a Classic system folder). If you have lots of drive space you may want to create an additional partition of 1 GB for future use as a swap partition to improve your system performance (see the osxfaq page for directions on changing the location of your swap files).
Try your installation...I hope it works for you...now you can try adding your RAM/3rd party devices back to the machine (my third party RAM could not tolerate the install but works fine after the fact) to see which ones are accepted.
Finally enjoy your new OS
p.s. I found a huge increase in system performance with 256 vs 128 MB of RAM that was related to reducing the use of the swap files. Ram is cheap now and well worth it. I have not yet tried the special swap partition but it makes soooo much sense that I'm sure it will add real performance improvements, especially to machines with little ram.
Mac OS X Hints