Failure to boot install-disk from SCSI CD-ROM drive.

[John Aspinall]

I'm trying to do a Mandrake 9.0 install from CD.  The machine in question is an old Pentium 1 with two disks and a CD-ROM drive, all on its SCSI chain.  The SCSI diagnostics check out ok, and the machine will boot Windows without a problem.  The CD itself
works to boot on a different machine.  I set the CD-ROM drive first in the preferred boot order with the BIOS.

I'm guessing here, but it looks like the boot loader loads ok.  But then I get the following:

ISOLINUX 1.76  Mandrake Linux isolinux: Loading spec packet failed, trying to wing it...
isolinux: Failed to locate CD-ROM device; boot failed.

The obvious question: can anyone shed light here?

Thanks in advance,
 John Aspinall