If you're adventurous, you could attempt replacing the internal optical drive with one from Other World Computing. This is an Apple/OEM drive, made by Matshita/Panasonic. It comes with installation instructions, and there's a link on that page to their installation videos. The only video I found there for an iMac G5 was for the non-iSight model, but it will give you a good idea of the difficulty involved and whether you'd want to try it. Otherwise, I'd suggest an external drive - their multi-connectivity (eSATA/FireWire/USB) DVD±RW drive, since it provides the Mac-preferred booting by FireWire. It has been my experience that some third-party drives don't respond to the keyboard command or the Startup Manager, when attempting to boot from the optical drive. In addition to the optical drive itself, the controller chip used on the enclosure's bridge board makes a difference, in terms of Mac-compatibility. OWC chooses and tests their products accordingly. You could try a less-expensive, third-party USB 2.0 DVD±RW drive from a PC/electronics store and see if it's bootable, but there's no way to tell in advance unless the manufacturer's specs indicate such. If you buy an optical drive from OWC, I'd take them up on their $29.00 special on the "Toast Titanium 11" software. For Macs, it's the best choice in CD/DVD burning software.
