To make it kind of a challenge, the Powerbook Aluminum 12'' was addled by a small HD, a slightly bent case, little RAM and a coffee-soaked combo drive.
Good news: most standard notebook HDs, RAM and slot-in optical drives (remove the slot facing on the replacement drive) fit, and Linux ought to run OK an a New World ppc.
Specs (L*W*H, in mm): optical drive 129*128*12.7, HD 100*70*9.5 ATA, RAM: SO-DIMM PC333 (2700) DDR, only one slot.
Bad news: you have to disembowel your powerbook completely to get at the optical drive, including removing the mainboard, detaching the heat sink and managing over 50 ridiculously small screws. Hard disk replacement happens on the way. Check the ifixit guide.
Additional things to have at the ready: ground bracelet (exposed mainboard and processor, remember), tweezers for lost screws etc, thermal conductivity paste, a soldering iron (for accidentally ripped cable connectors). A big hammer. Patience. Bravery. Faith.
Actually, the ifixit guide comments the necessary removal of a few keyboard keys with: This is scary - take a deep breath before continuing. A few pages later, you get such laconic gems as Support the heat sink with both hands, and carefully lift it out of the computer, or Lift the logic board partly up from the optical side - without any further encouragement. God, I need a shrink now.
Tisiphone (Samsung R55 Cavan) got a hard drive upgrade parallelly: a matter of two screws and one cable…
After that, everything went OK: We left 50 GB for Linux in the Apple partitioner. By patiently pressing "C" during bootup, the Powerbook was persuaded to boot both a Kubuntu hardy ppc CD and a SuSE 11.1 ppc DVD, though we haven't got around to installing anything yet.