So I finally took the plunge and took a Torx screwdriver to my beloved Mac.  Didn't know what a Torx screwdriver was until I took the baseplate off and found that I couldn't go any further, thanks to asterix-shaped screws!  But a day later I was properly ready. 

It was incredibly dusty inside!  Despite being incredibly tightly packed with components, I had to blow out a lot of fluff just to be able to see where I was going.  Eventually managed to disengage various cables and ease out the Superdrive with its piggy-backed hard drive.  Phew!

The replacement components are slimmer than the originals, but still had a bit of a fight getting them in, and had to take the faceplate off the DVD burner.  Nearly forgot to apply the thermal paste, which I bought especially; hard to believe it does anything…

And heart in mouth, I plugged it back in and pressed Power.  Hooray!  She still works.  Sadly, the burner isn't recognized, so looks like I'll have to go back in and see what I've done wrong – I suspect it's the "jumper".  I didn't really know what one was until I looked for it, expecting some sort of switch.  I sorted it out on the hard drive, but forgot there was one on the burner as well.

But my iMac G4 now has 160Gb of hard drive space!  If I can just get the burner to work, hopefully it'll fix my DVD burning issue…