Powerbook g4 restart message

Assuming your system is not the original Powerbook (since the hardware test can be downloaded), no, you can no longer buy the OS X disks that came with PowerBooks.

The closest thing today you can buy is TechTool Pro, which does hardware testing and much more. If you had Applecare on the Powerook, you can download TechTool Deluxe from the Apple site.

If you just want to test the memory, rember is a good program. Let it run overnight.

That's a kernel panic which is usually, but not always, caused by hardware, with memory the leading cause. Reseat the memory, then run theApple hardware test. When prompted, run the extended test.