even after a lot of fiddling around, the methods above didn’t work for me. But I finally got to install Linux in the 2008 Macbook white! Here’s what worked for me: I installed the laptop HDD into my old Win7 core2duo desktop and booted off the Lubuntu 18.04 DVD I had. I installed the OS, then turned it off and simply transferred the HDD into my Macbook. And voila! My Macbook now boots into Linux! Everything works. I later installed LibreOffice and Zoom for Linux. LibreOffice was no problem, but Zoom asked for a lot of dependencies (Lintian, and dozens of other files that the installer fortunately listed). I am a very happy camper! Now to do the same for my other two Macbooks.
Update: I removed the bloated battery but still can’t boot from the SSD. It’s probably corrupted. So I booted from the USB stick I had for late 2010 Mac Airs and formatted the main drive (Mac OS Journalled). I tried to restore the OS (using Disk Utilities) from the hidden partition containing the factory disk image in it but still no joy. I ended up installing the original Snow Leopard OS from the USB stick into the main partition and now everything works.
Problem solved! I have done some more research in the past days and found that the format I did on the hard drive in target mode defaults to Master Boot Record (MBR). Powerbooks can boot only from drives formatted with Apple Partition Map (APM). So, I redid the erase command from Disk Utility and went into the Advanced options below the screen, selected one partition choice, clicked on APM, and proceeded to erase. A new cloning of the drive fixed the issue and now allows the Powerbook to boot from its own drive. Now to get a proper install disk. Yes, thanks for the tip, Mayer, I know iBooks and Powerbooks can be upgraded to Leopard if the processor runs 867 MHz or faster. RAM should be 1 GB or more to run them fluidly.
Well, I did boot up my powerbook in target mode, connected it by firewire cable to the iBook, power up the iBook and immediately pressed <option> key. Shortly, the ibook screen showed the 2 bootable OS'es. I chose the powerbook hard drive, but there's no change. The iBook screen still goes dark and the machine goes into hibernation. Looks like it's really a logicboard problem.
Update: A 600 MHz G3 iBook was brought to me. Symptom was it gets perpetually stuck in the opening screen with the Apple logo and spinning wheel icon on boot. Hard drive problem with OS, I surmise. So I connect it to my Powerbook via a firewire cable and boot it in target mode. It doesn't mount. So I launch Disk Utility and the bad iBook HDD shows up in it. I erase it with the Utility tools, and everything seems good. I try to clone my Powerbook HDD to it with SuperDuper! but after 80% of the process is done I get an error message and the process aborts. Looks like the target HDD finally gave up the ghost.