it's rather easy to replace the drive. It's much like the tray-loading iMac. All the actual computer components are on a tray that when you take the screws out of it, it just comes with it. The dvd drive is fairly easy to remove.

Also, when the G4s came out, at least the later ones, they seemed to have remove USB Booting support. Yes, it does it on the PowerMacs, but USB 2.0 and later USB 1.1 models won't boot. Not sure why, it seems to be that they did this when they switched over to 10.3 or so, but that's when they decided to remove support.

It seems that G3's starting with the AGP Models seems to have had USB boot support, but that's mainly because they have USB 1.1

Sorry man, it looks like you can't boot from USB. however... If you have laptop or PowerMac that you can turn into a FWTDM, you can put the CD/DVD in it, hook it up to the eMac and boot from the Optical drive on the laptop/powermac, as it will let it be seen over the FireWire connection

I did this with an iBook that had a bummed DVD/CD-RW drive before apple got it for the last time and replaced it, but I was able to reinstall the system after putting my Pismo into FWTDM and hooking it up through the FireWire port and booting off the optical drive from the Pismo.

I dunno what to say, but you can go into it fairly easy. Although the CRT isn't shielded, if you work from the underneath of it, you won't get your hands even CLOSE to the high voltage area. There is no reason to be on the other side of the sled

Best of luck!

coius