The problem with the PowerBook has been confirmed to be the RAM upgrade I put in back in 2004. It hummed along fine for 3½ years, but I guess it finally went bad with the laptop getting so much more use the last few weeks.
Better something modular and easy to get at (well, except for the one stripped screw) than something intrinsic to the machine. Under the circumstances, I’m just having the shop replace it.
Though I guess I should’ve known better than to trust this guy:
moar humorous pics
(Check out the original lolcat post if you don’t recognize the phrasing.)
Assuming the box continues to pass diagnostics with the new memory, I should be able to pick it up at lunch on Monday.
Update: Success! The computer is back, and working again!