I feel Really Stupid.
You see, when I started using 2.6 kernels (currently 2.6.11), I also started getting told ide-scsi is deprecated, use ide-cd instead
when I burned CDs. Eventually I decided to do something about it and left ide-scsi out of my kernel.
Well, after that I couldn't manage to burn a CD, and even when I tried to use ide-scsi again, it wouldn't work. I couldn't find any information about my problem, and in any case I could burn CDs in Windows. I couldn't burn CDs in Linux for months.
Today Jeff wanted to burn a Darwin (PPC) ISO to CD. He doesn't have a CD burner, so I burn things for him on Delilah. No biggie, except Easy Coaster Toaster barfed on the non-ISO9660 image. Drat.
I rebooted into Linux and poked around on the Web. Turns out the cdrecord options for burning with ide-cd are a little different from burning with SCSI emulation, so I try cdrecord dev=/dev/hdc darwinppc-801.iso — but no cigar. I think I'd tried that before, and it still doesn't work. Just for laughs, I tried hdb, and what do you know, it actually worked! Huzzah!
The solution was so bloody easy that I overlooked it for months. I feel like a complete idiot. My only consolation is that I hadn't gotten around to asking on debian-user.