Well I took the plunge, tore apart my PowerBook G4. I had instructions from PBFixit.com. Excellent instructions. Showed pictures with little colored circles showing what screw to remove. Every time I took a little screw out I taped it to the paper.
No problem getting the hard drive out--basically remove the keyboard and top cover, and there you are. But the optical drive was a different matter. In fact, I couldn't do it. When I got to the step where I was supposed to remove two spring-loaded screws to release the heat sink, I couldn't get one of them out. It was sort of a hollow thing that screws onto a threaded post underneath. One of them came out fine, but the second would only loosen. It would not come off. So I was stuck. Ah well it all went back together ok and I'm up and running with a new 100 GB hard drive.
I put my old one into a little "FireXpress" hard drive case "slim storage by CompuCable". Such a nice little aluminum case. I put the new 8x dual layer DVD burner into an external "Digistor" case. Both are so nice and compact.
Oh yeah when I first got the hard drive and case, I put the new one in the external case, and then used Disk Utility to "restore" my old hard drive onto the new hard drive. Then I tested that it would boot ok, which it did. Then I swapped the hard drives. Slick as a whistle.
These small external media cases are so cool.
Oh yeah I forgot to say I also bought some audio stuff--an iMic by Griffin. Nice piece of hardware, provides improved quality of output over the built-in headphone jack (at least it seems that way to my untrained ears), and also provides low level and line level microphone inputs. That will be nice because I'm still working on digitizing my LP and cassettes.
Bought a nice little microphone on eBay. It's basically just a gold-plated 1/4 inch plug with a microphone mounted in the end and a wind-screen. I think combined with the iMic it will provide high quality audio input to the computer.