I'm planning on buying a new drive, but in the meantime, I figured there must be some way to disable the drive from software. I didn't want to screw up my machine just by accidentally opening up the System Profiler, and I didn't want to take apart the laptop and disconnect it. I couldn't find any documentation on how to disable the inernal drive via Open Firmware's nvram settings, but I did find one approach that actually worked: removing the IODVDStorageFamily extension (IODVDStorageFamily.kext bundle) from /System -> Library -> Extensions.
I simply created a new folder called DisabledExtensions and dropped it there. There's also an IOCDStorageFamily extension, presumably if you're using a plain-old CD-ROM drive, you'd want to nuke that one.
After moving the extension, I rebooted and confirmed that the drive no longer showed up (nor did it cause hangs) when opening System Profiler or other applications that want to interact with the optical drive.

