I had to get a different DVD drive for my external USB enclosure, it turned out that the one I had was completely incapable of seeing a CD-R. Very strange, given that the DVD drive was a DVD-RW drive.. Being a burner, you'd think it'd be able to read burnt media.. But nope.. I confirmed this by plugging the USB cable into a properly working computer that was already booted up. I inserted the CD and it never saw it. But it booted DVD's just fine.. Very strange.. Ended up yanking a DVD drive out of one of the dead iMac's in my garage and sticking it into my USB enclosure. That did the trick.