Each machine has just one CD-ROM drive (they're actually fairly recent DVD drives). Now that I'm in front of the machine and have tried it again, this is what I get:
Drive name from proc filesystem: hdb
Searching for hdb: . .. hdb Matches!
Found line for device ide0
Major version number for device ide0 is 3
Probably found CD-ROM
Unable to identify CD-ROM format.
Startup failed: Invalid argument