If the disk is physically installed in your machine and Linux recognises it, try mounting it using the 'sysv' filesystem type, i.e.
[tt]mount -o ro -t sysv /dev/sda1 /mnt[/tt]
I'm just guessing here; I've never tried it. I'm not sure whether 'sysv' and HTFS, which OpenServer normally uses, are equivalent. Annihilannic.